People v. Thompson, 2017 IL App (3d) 160503

In Sept. 2015 two deputies encountered Jeremy Thompson outside an apartment; Thompson pointed a .22-caliber pneumatic rifle with a green laser at officers and later told them he hid the gun; officers recovered the unloaded pneumatic rifle about 40 feet away.
Thompson was charged with (1) possession of a firearm by a felon, (2) aggravated assault for shining a laser sight, and (3) aggravated assault for pointing a firearm at an officer.
The State called Det. Sgt. Adam Diss to testify about muzzle velocity using a personal chronograph; Diss fired 10 pellets and reported velocities of 714–741 feet/sec (over the 700 fps statutory threshold).
On cross-examination Diss admitted he had no formal forensic training, did not calibrate the chronograph, did not follow or know applicable industry/national standards, did not fix the gun during testing, and did not record environmental conditions; he checked his device only against friends’ chronographs and factory loads.
The trial court admitted Diss’s chronograph results over defense objection; the jury convicted Thompson on all counts and he received a two-year sentence.

Issue	Plaintiff's Argument	Defendant's Argument	Held
Admissibility/foundation for expert testimony based on chronograph results	Diss’s experience and his test results are admissible; chronographs are industry standard for measuring muzzle velocity	Insufficient foundation: no calibration, no adherence to accepted methodology, unreliable device/results	Court abused its discretion admitting Diss’s ballistics testimony because foundation for the device and methodology was not established
Remedy / Double jeopardy / Sufficiency of evidence without improper testimony	Retrial is permissible if, including improperly admitted evidence, the record would allow a rational trier of fact to convict	If evidence without the improper testimony was insufficient, double jeopardy would bar retrial	Although Diss’s testimony was erroneously admitted, the total evidence (including that testimony) was sufficient to permit retrial; conviction reversed and case remanded for new trial

People v. Bynum, 257 Ill. App. 3d 502 (foundation required to show testing device was functioning properly)
People v. Raney, 324 Ill. App. 3d 703 (expert must show machine was working properly and accuracy established)
Washington v. Police Board of the City of Chicago, 257 Ill. App. 3d 936 (testimony about calibration and machine functioning supports admissibility)
People v. DeLuna, 334 Ill. App. 3d 1 (daily calibration testimony supports GCMS results admissibility)
People v. Berrier, 362 Ill. App. 3d 1153 (calibration before testing supports admissibility)
People v. Olivera, 164 Ill. 2d 382 (double jeopardy principles on retrial after reversal for trial error)
People v. McKown, 236 Ill. 2d 278 (retrial appropriate if evidence presented at first trial— including improperly admitted evidence—would allow a rational factfinder to convict)
People v. Williams, 238 Ill. 2d 125 (abuse of discretion standard for foundational challenges to expert testimony)