Forensics testimony ties Ashbaugh DNA, gunshot-residue evidence to items recovered in officer-involved shooting case

Forensic scientists testified at a Bexar County hearing that laboratory analyses linked items collected from a vehicle and a pistol to defendant Tyler James Ashbaugh in San Antonio Police Department case 22108229, an officer‑involved shooting investigation.

Caitlin McCaughn, a forensic scientist in the Bexar County Criminal Investigation Laboratory’s serology and DNA section, testified that she screened items submitted under lab case number 22‑03151 to identify candidates for DNA testing. McCaughn said the lab’s serology work determined which swabs were suitable for touch‑DNA testing but that conventional serology for blood, semen or saliva was not performed on those items.

Robert Sailors, a forensic scientist and supervisor in the lab’s biology department, told the court he performed DNA analysis on swabs from vehicle surfaces and a known standard from Ashbaugh. He said the gear‑shift swab (item E12) produced DNA consistent with four contributors and that the genetic typing “is approximately 21 septillion times more likely if they had originated from Tyler James Ashbaugh and three additional people than if they originated from four unknown unrelated individuals.” Sailors said the interior driver‑door handle swab (E13) showed DNA consistent with three contributors and the results were “about 97 quintillion times more likely” if Ashbaugh were a contributor. On a pistol swab (E3A), Sailors said he could identify a major contributor and that Ashbaugh “was not excluded as the major contributor” and that the random‑match probability for that profile was on the order of 1 in 23 septillion.

Mary Bowen, a forensic scientist supervisor in the lab’s gunshot‑residue (GSR) unit, testified about particle counts from clothing and a GSR kit taken from the defendant. Bowen said the navy blue T‑shirt submitted in evidence had 10 microscopic particles containing lead, barium and antimony on the front right chest and 10 on the front left; she described that result as supporting the conclusion that the T‑shirt “may have come in contact with a discharged firearm or was in close proximity to a discharging firearm.” Bowen said the pair of gray pants and a red polo and red T‑shirts had fewer or indeterminate particles; she also testified that the GSR sampling device taken from Ashbaugh’s right hand contained one microscopic particle with lead and antimony and that no particles were detected on his left hand. Bowen said the single particle on the right hand led to the lab conclusion that Ashbaugh “may have discharged a firearm, handled the discharged firearm, or was in close proximity to a discharging firearm.”

Detective Chad Tudor of the San Antonio Police Department’s homicide/murder detail described investigative steps and video evidence. Tudor testified that church parking‑lot surveillance shows a white sport utility vehicle drive onto the lot and that he observed audio and a frame‑by‑frame image consistent with a muzzle flash near the driverside of a marked patrol vehicle at video timecode the report records as about 00:02:01. Tudor said he sought and obtained a search warrant for the Nissan Rogue associated with the case and later obtained a warrant for a buccal swab from Ashbaugh; he also said he obtained arrest warrants for aggravated assault on public servants naming officers Philip Haines and Roland Acuna as victims.

The court admitted multiple lab and scene exhibits during the hearing, including the GSR kit collected from Ashbaugh, clothing samples and the church surveillance video. Laboratory reports entered the record show: the serology screening report released 09/15/2022, the DNA report released 09/11/2023, and a GSR report released 10/28/2022. Tudor told the court that the phone‑data and cell‑tower information investigators obtained placed Ashbaugh in the area of the incident and said the lab comparisons and video analysis supported the prosecution’s case theory.

Defense counsel cross‑examined witnesses about the limitations of mixture interpretation, the meaning of a single microscopic GSR particle, and the relative distances in the surveillance video. Experts acknowledged technical limits: Sailors explained the lab’s use of probabilistic genotyping for mixtures and that a “not excluded” result does not mean uniqueness beyond the reported statistical weight; Bowen reiterated that GSR cannot distinguish between having fired a weapon and having been near a discharge.

Prosecutors and detectives said laboratory evidence, the video, and phone‑data were being combined with witness interviews and physical evidence to present the case to a jury. The hearing record shows the prosecution offered the lab reports and surveillance footage into evidence and that the judge admitted the items without objection in the instances noted on the record.

The case remains pending; detectives said they continue to process digital and physical evidence for trial.