308 So.3d 193
Fla. Dist. Ct. App.2020Background
- On Jan. 4, 2013, two masked robbers entered a closed restaurant, robbed patrons, and fatally shot the owner’s boyfriend; a Chopard watch taken at the robbery was later sold at a convenience store.
- Police recovered a 9mm bullet/casing and a 9mm pistol; DNA from the pistol and the watch matched appellant Samuel Walker; Walker admitted knowing the co-defendants and being in the convenience store (surveillance ID).
- Phone records (tower IDs and timestamps) for Walker and codefendants were admitted; a detective used TRAX mapping software to produce cell-site coverage diagrams showing the phones in the restaurant area at the crime time and at the convenience store when the watch was sold.
- The detective had ~100 hours training, >200 mapping cases, >10 prior testimony appearances, and performed recent drive‑testing/field scans asserting the software’s accuracy, but he did not know the TRAX algorithm or a numeric error rate.
- Defense moved to exclude the detective’s testimony under Daubert/§90.702; the trial court admitted the testimony and the jury convicted Walker of first‑degree murder and multiple robberies; the Fourth District affirmed, holding the trial court did not abuse its gatekeeping discretion.
Issues
| Issue | Plaintiff's Argument | Defendant's Argument | Held |
|---|---|---|---|
| Admissibility of detective’s cell‑site mapping under Daubert/§90.702 | Testimony unreliable because detective lacked knowledge of TRAX algorithm and error rate | Detective’s training, experience, and drive‑tests provide sufficient reliability; TRAX output shows approximate coverage, not precise location | Affirmed: trial court did not abuse discretion; testimony admissible; expert not required to know underlying algorithm; other indicia suffice |
| Whether testimony was expert or non‑expert (Gordon/Perez analogy) | Mapping using software required expert qualification and Daubert analysis | Comparable to factual explanatory testimony in Gordon/Perez; in any event, testimony met Daubert | Court: even if treated as expert, testimony satisfied Daubert; parallels to Gordon/Perez support admissibility |
Key Cases Cited
- Daubert v. Merrell Dow Pharm., 509 U.S. 579 (gatekeeper role; factors for reliability)
- Kumho Tire Co. v. Carmichael, 526 U.S. 137 (Daubert factors are flexible and apply to all expert testimony)
- Gordon v. State, 863 So. 2d 1215 (Fla. 2003) (cell‑record explanatory testimony treated as non‑expert)
- Perez v. State, 980 So. 2d 1126 (Fla. 3d DCA 2008) (custodians’ cell‑site testimony as general background explanation)
- McMillian v. State, 214 So. 3d 1274 (Fla. 2017) (principles of cellular technology broadly accepted)
- United States v. Morgan, 292 F. Supp. 3d 475 (D.D.C. 2018) (investigators may rely on software outputs without knowing underlying code)
- Williams v. State, 606 S.W.3d 48 (Tex. App. 2020) (admission of cell‑site plotting despite unknown error rate not an abuse)
- United States v. Hill, 818 F.3d 289 (7th Cir. 2016) (historical cell‑site analysis has generally been admitted)