¶ 1 Petitioners in these cases were charged with drug offenses following traffic stops and the discovery of drugs in the cars in which they were traveling. They claim that the police officers who stopped the vehicles were engaged in “racial profiling,” the selective enforcement of traffic laws based on race. The issue before us is whether the defendants are entitled to the appointment of an expert witness to assist them in proving this allegation.
I.
¶2 Petitioners Anthony James Jones, an African-American, and Luis Rodriguez-Bur-gos and Jose Altagracia Rodriguez, both of whom are Latino, were in vehicles stopped by Department of Public Safety (“DPS”) officers on 1-17 in Yavapai County on separate occasions in 2001 and 2002 as part of a statewide drug interdiction effort. In each case, DPS officers discovered drugs inside the vehicles. Petitioners were thereafter arrested and charged with drug offenses.
¶3 Petitioners claimed in the superior court that the DPS officers had selectively enforced traffic laws against them and other African-American and Latino motorists and
¶ 4 The defendants first sought document discovery from the State to support their racial profiling claim. They offered testimony by Dr. Frederic I. Solop, Director of the Social Research Laboratory at Northern Arizona University, in support of that application. Dr. Solop said that his preliminary analysis of data about the race of motorists stopped by DPS in Yavapai County and data on the racial composition of motorists violating traffic laws in general led him to conclude that a colorable claim of selective enforcement existed. The superior court granted the discovery motion.
¶5 Defendants later moved pursuant to Arizona Rule of Criminal Procedure 15.9(a) for appointment of Dr. Solop as an expert witness. The superior court denied the motion, holding that the alleged selective enforcement of traffic laws was not a defense to the drag offenses for which the defendants were charged and that the appointment of an expert therefore was not “reasonably necessary to present a defense” as required by Rule 15.9(a).
¶ 6 Petitioners sought special action relief in the court of appeals, which declined jurisdiction. We granted the petition for review because the issues presented are of statewide importance and first impression. 1 We have jurisdiction pursuant to Article 6, Section 5(3) of the Arizona Constitution and Arizona Revised Statutes (“A.R.S.”) § 12-120.24 (2003).
II.
¶7 Arizona Rule of Criminal Procedure 15.9(a) provides:
An indigent defendant may apply for the appointment of an investigator and expert witness ... to be paid at county expense if the defendant can show that such assistance is reasonably necessary to present a defense adequately at trial or sentencing. The central issue in this case is whether petitioners’ selective enforcement claims could constitute a “defense” to the pending criminal charges.
A.
¶ 8 In concluding that selective enforcement of the traffic laws was not a defense to the drag crimes with which petitioners are charged, the superior court primarily relied on
Whren v. United States,
¶ 9 The
Whren
defendants, both of whom were African-American, conceded that the officers had probable cause to believe that traffic laws had been violated.
Id.
at 810,
¶ 10 The Supreme Court unanimously rejected the argument “that the constitutional reasonableness of traffic stops depends on the actual motivations of the individual officers involved.”
Id.
at 813,
¶ 11 Decisions after
Whren
have confirmed that evidence seized as a result of a traffic stop meeting “normal” Fourth Amendment standards is not rendered inadmissible because of the subjective motivations of the police who made the stop.
See Devenpeck v. Alford,
B.
¶ 12 Whren, however, did not approve selective enforcement of traffic laws, nor did it hold that proof of such selective enforcement is irrelevant in the defense of a resulting criminal case. Rather, Justice Scalia, writing for a unanimous court, emphasized:
We of course agree with petitioners that the Constitution prohibits selective enforcement of the law based on considerations such as race. But the constitutional basis for objecting to intentionally discriminatory application of laws is the Equal Protection Clause, not the Fourth Amendment.
Whren,
¶ 13 As Justice Scalia noted in
Whren,
it is beyond contest that race-based selective enforcement of the law violates the Equal Protection Clause of the Fourteenth Amendment.
Id.
“Racially selective law enforcement violates this nation’s constitutional values at the most fundamental level; indeed, unequal application of criminal law to white and black persons was one of the central evils addressed by the framers of the Fourteenth Amendment.”
Marshall v. Columbia Lea Reg’l Hosp.,
¶ 14 The State’s briefing readily and correctly concedes this. The State contends, however, that proof of selective enforcement of traffic laws is not a defense to a criminal charge, but rather entities injured parties only to civil redress pursuant to 42 U.S.C. § 1983. It therefore argues that appointment of an expert to assist in proof of selective enforcement is not, in the words of Rule 15.9(a), “reasonably necessary to present a defense adequately at trial and sentencing.”
¶ 15 Selective enforcement of traffic laws on the basis of race can give rise to a § 1983 claim.
See, e.g., Johnson v. Crooks,
¶ 16 The seminal case is
Yick Wo v. Hopkins,
¶ 17 The Supreme Court noted that the underlying ordinance was faciady neutral as to race: it was “fair on its face, and impartial in appearance.”
Id.
at 373,
[T]he facts shown establish an administration directed so exclusively against a particular class of persons as to warrant and require the conclusion that, whatever may have been the intent of the ordinances as adopted, they are applied by the public authorities charged with their administration, and thus representing the state itself, with a mind so unequal and oppressive as to amount to a practical denial by the state of that equal protection of the laws which is secured to the petitioners, as to all persons, by the broad and benign provisions of the fourteenth amendment to the constitution of the United States."
Id.
at 373,
¶ 18 Although the selective enforcement claim in Yick Wo was somewhat different than the one here, the case squarely stands for the proposition that violation of the Equal Protection Clause by authorities enforcing a facially neutral law can result in dismissal of resulting criminal charges. As the Court put the matter:
Though the law itself may be fair on its face, and impartial in appearance, yet, if it is applied and administered by public authority with an evil eye and unequal hand, so as to practically make unjust and illegal discriminations between persons in similar circumstances ... the denial of equal justice is still within the prohibition of the constitution.
Id.
at 374,
¶ 19
Whren
does not call the basic holding of
Yick Wo
into question. Indeed, numerous decisions after
Whren
have treated selective enforcement of facially neutral traffic laws as a potential defense to non-traffic criminal charges arising from a traffic stop.
See, e.g., United States v. Barlow,
C.
¶20 The State also contends that even if § 1983 does not provide the exclusive remedy for selective enforcement based on race, proof of such conduct is nonetheless not a “defense” for purposes of Rule 15.9(a). The State relies primarily on
United States v. Armstrong,
¶ 21 The Supreme Court first considered whether the requested discovery was mandated by then Federal Rule of Criminal Procedure 16(a)(1)(C), which required disclosure of items “material to the preparation of the defendant’s defense.”
See id.
at 461-62,
¶22 We decline that invitation. As an initial matter, it is important to note that
Armstrong
did not hold that the Fourteenth Amendment cannot be raised as a defense in a criminal trial. To the contrary, while rejecting the notion that disclosure of certain materials in support of such a claim was mandated by Rule 16(a)(1)(C), the Court reviewed in detail the standards of proof applicable to Fourteenth Amendment claims of selective prosecution.
Id.
at 463-68,
¶23 More importantly, we believe that the term “defense” in Rule 15.9(a) is not limited to what the Court in
Armstrong
called a “defense on the merits,” but is intended to encompass the common understanding of the term — “any set of identifiable conditions or circumstances which may prevent a conviction for an offense.” Paul H. Robinson,
Criminal Law Defenses: A Systematic Analysis,
82 Colum. L.Rev. 199, 203 (1982);
see also
Black’s Law Dictionary 430-31 (7th ed.1999) (defining “defense” as “[a] defendant’s stated reason why the ... prosecutor has no valid case”). Our conclusion is supported by the structure of Rule 15. For example, Rule 15.2(b) requires a defendant to “provide a written notice to the prosecutor specifying all defenses as to which the defendant intends to introduce evidence at trial, including, but not limited to, alibi, insanity, self-defense, defense of others, en
trapment,
¶ 24 This broad reading of Rule 15.9(a) finds additional support in the language of the Rule itself. The Rule allows appointment of an expert when the defendant can show “that such assistance is reasonably necessary to present a defense at trial or sentencing.” (Emphasis added.) A defendant does not, of course, present a defense on the merits at sentencing; he instead argues for leniency. Because the Rule expressly contemplates that such arguments qualify as a “defense,” arguments of constitutional violations deserve no lesser treatment. 7
D.
1125 The State next argues that Rule 15.9(a) permits only the “appointment of experts to be used at trial on defense issues, not on pre-trial issues, such as the one involved in this litigation.” We do not read the phrase “at trial or sentencing” in Rule 15.9 so narrowly. Instead, that phrase encompasses the whole of a criminal proceeding at the trial court: the pretrial phase, the trial phase, and the judgment and sentencing phase.
1126 In this case, the petitioners seek the services of an expert in support of a motion to dismiss or, in the alternative, a motion to suppress. While it is true that a defendant must normally make these motions before trial, Ariz. R.Crim. P. 16.1(b) and (c), nothing precludes a trial court judge from deferring ruling on a Rule 16 motion until after trial begins. Cf. Ariz. R. Crim P. 16.3(e) and (d) (allowing a trial judge to take additional evidence on motions at proceedings “subsequent” to an omnibus pretrial hearing).
¶ 27 More importantly, the States reading of Rule 15.9(a) would present potentially serious constitutional concerns. The denial of expert witness assistance to a criminal defendant can violate the Due Process Clause of the Fourteenth Amendment.
See Ake v. Oklahoma,
III.
¶ 28 For the reasons above, we hold that the superior court erred in concluding that a showing of selective enforcement can never be a defense to a criminal prosecution. It does not follow, however, that the superior court must grant the Rule 15.9(a) application before it in these consolidated cases.
¶29 Rule 15.9(a) mandates the appointment of an expert witness only when “such assistance is
reasonably necessary
to present a defense adequately at trial or sentencing.” (Emphasis added.) We have held, in interpreting substantially identical language in the statute governing appointment of experts in capital eases, that the decision rests in “the sound discretion of the trial court.”
State v. Gretzler,
¶30 The determination of what is “reasonably necessary” to prove selective enforcement requires at the outset an analysis of the elements of such a claim. Because a selective enforcement claim rests on an assertion that the Equal Protection Clause has been violated, the claimant must demonstrate that state action “had a discriminatory effect and that it was motivated by a discriminatory purpose.”
Armstrong,
¶ 31 As the Supreme Court emphasized in
Armstrong,
this Fourteenth Amendment test imposes a “demanding standard” of proof as a “significant barrier to the litigation of insubstantial claims.”
Armstrong,
¶32 Caution is also required because a selective enforcement or selective prosecution claim is easily asserted, and responding to such a charge may be expensive, time consuming, and unduly distracting.
See Armstrong,
¶ 33 We believe that the
Armstrong
standard, although articulated in the context of discovery, is equally appropriate in evaluating requests under Rule 15.9(a) for the appointment of experts to prove selective enforcement claims. In such cases, the trial court should determine whether the defendant has presented credible evidence of both discriminatory effect and intent before appointing an expert. Moreover, in determining whether an expert is “reasonably necessary,” the superior court may consider that “[w]hile helpful, purely statistical evidence is rarely sufficient to support an equal protection claim.”
Mesa-Roche,
¶ 34 In addition, a superior court confronted with a Rule 15.9(a) motion in a case like this should make at least preliminary inquiry as to the nature of the statistical evidence that a defendant hopes to produce before determining whether an expert will be “reasonably necessary” to present a defense. To support a Fourteenth Amendment claim, statistics must be both “relevant and rehable.”
Barlow,
IV.
¶ 35 In the case before us, the superior court has not yet had the occasion to analyze the defendants request for an appointment of an expert under the standards articulated above. Although the defendants claim to have credible evidence of both discriminatory effect and discriminatory intent and assert that the proposed study will produce relevant and reliable information, it is not appropriate in the context of this case for us to evaluate those claims in the first instance. Therefore, while we vacate the order of the superior court denying the application of the defendants for appointment of an expert, we remand to the superior court for further proceedings consistent with this opinion.
Notes
. The superior court stayed its proceedings to allow petitioners to seek special action relief. We subsequently granted a similar stay pending our disposition of this matter.
. The Court noted that Yick Wo and the defendant in the consolidated case "have complied with every requisite deemed by the law, or by the public officers charged with its administration, necessary for the protection of neighboring property from fire, or as precaution against injury to the public health.”
Yick Wo,
. Similarly, courts have long entertained Fourteenth Amendment "selective prosecution" challenges to criminal prosecutions.
See, e.g., Wayte v. United States,
. Selective enforcement and selective prosecution claims are both governed by the analysis generally applicable to Equal Protection claims.
Barlow,
. In 2002, Rule 16(a)(1)(C) was relettered as Rule 16(a)(1)(E) and stylistically amended.
. Similarly, while a defendant’s claim that prosecution was barred by the statute of limitations or double jeopardy would likely not meet the Armstrong definition of a "defense on the merits,” each surely falls within the broad category of “defenses” for which notice is required under Rule 15.2(b).
. The State also argues that because common law affirmative defenses have been abolished in Arizona, see A.R.S. § 13-103(A) (2001), selective enforcement cannot be a "defense” for purposes of Rule 15.9(a), as it is not provided for by statute. Section 13-103(A), however, plainly cannot prevent a defendant from raising constitutional defenses to a criminal charge. A selective enforcement claim, as Whren makes clear, arises under the Fourteenth Amendment, not under Arizona statutes or the common law.
. For example, in this case copying costs for discovery are already nearly $7,000; the cost of completing the requested study has been estimated at anywhere between $10,000 and $72,000; and some of the consolidated defendants in this case were indicted nearly four years ago but have not yet proceeded to trial.
. While statistics conceivably could prove discriminatory effect in some cases,
see Chavez,
. In contrast, in
Mesa-Roche,
the court found discriminatory effect after analyzing studies that accounted for both the "transient motor population" and “violator” benchmarks.
