Coffin v. Superintendent, Massachusetts Treatment Center, 458 Mass. 186

In 2001 Coffin was charged with indecent assault and battery on a person over 14 and pled guilty; he received one year in the house of correction and lifetime parole for life under G. L. c. 275, § 18 and c. 265, § 45.
Coffin violated parole terms several times, with each violation leading to incarceration.
He then pled guilty to breaking and entering and received a three-month house of correction sentence.
After release, Coffin violated parole a fourth time and in October 2005 was ordered to serve one year for parole violation.
On September 14, 2005, this Court decided Commonwealth v. Pagan, holding lifetime parole procedures unconstitutional as applied; Coffin’s fourth parole violation custody overlapped with that decision.
On March 1, 2006, while still in custody and before ruling on vacating the lifetime parole sentence, the Commonwealth filed a § 12(b) SDP petition and Coffin was temporarily committed.

Issue	Plaintiff's Argument	Defendant's Argument	Held
Whether an unconstitutional sentence bears on § 12(b) prisoner status	Coffin argues he is not a "prisoner" under § 12(b) because his confinement was due to an unconstitutional sentence.	Commonwealth argues custody suffices to be a "prisoner" under § 12(b) even if sentence later deemed unconstitutional.	No; a person imprisoned under an unconstitutional sentence is not a § 12(b) prisoner.
Does ongoing custody while an unconstitutional sentence is in effect satisfy § 12(b)’s requirement	Custody exists but the sentence is invalid, so § 12(b) cannot attach.	Custody and ongoing confinement could still activate § 12(b).	Custody tied to an invalid sentence does not trigger § 12(b) eligibility.
Does a court’s invalidation of a sentence erase § 12(b) jurisdiction for that individual	Invalidation shows lack of prison status for § 12(b).	§ 12(b) applicability is independent of other statutes’ validity.	Petition to commit under § 12(b) is improper where sentence was facially unconstitutional.

Commonwealth v. Pagan, 445 Mass. 161 (2005) (unconstitutionality of lifetime parole procedures as applied to Coffin’s context)
Commonwealth v. Gillis, 448 Mass. 354 (2007) (limits of § 12(a) post-commitment; interpretation of prisoner status)
Commonwealth v. Allen, 73 Mass. App. Ct. 862 (2009) (custody alone not dispositive; need constitutionally sound sentence for § 12(b))
Chicot County Drainage Dist. v. Baxter State Bank, 308 U.S. 371 (1940) (voidable vs void; legal process required to remedy invalid conviction)
Robinson v. Neil, 409 U.S. 505 (1973) (valid confinement until reversed through legal process)