SAN FRANCISCO (AP) — The murder suspect at the center of a national immigration debate admits he fired the shot that killed a young San Francisco woman on an evening stroll with her father.

The question remains whether he purposely aimed the gun at Kate Steinle, 32, or accidentally fired the weapon.

The former head of the San Francisco Police Department crime lab testified in court Thursday that the shooting appeared to be accidental. Prosecutors and police contend that Juan Francisco Lopez-Sanchez was aiming to shoot Steinle when he pulled the trigger on July 1.

Investigators and ballistics experts earlier testified that the bullet ricocheted off the concrete pavement of the pier and struck Steinle in the back.

Jim Norris, the former head of the San Francisco police crime lab testified Thursday that it appears that Lopez-Sanchez was aiming when he fired. He also said the type of gun used — a .40 caliber Sig Sauer semi-automatic pistol stolen from a federal agent — had been at the center of several law enforcement accidental shootings.

Norris testified during the third day of a preliminary hearing held to determine if there’s enough evidence for Lopez-Sanchez to stand trial. The judge scheduled further proceedings for Sept. 3.

San Francisco police inspector John Evans testified Wednesday that the bullet traveled in a straight line, suggesting Juan Francisco Lopez-Sanchez was pointing the gun in the direction of Steinle.

Evans testified Wednesday that investigators found a spot on Pier 14 where a bullet left a mark on July 1 before striking Steinle in the back as she walked with her father. San Francisco medical examiner Michael Hunter also testified Wednesday that the bullet made a rectangular-shaped wound rather than a typical oval-shaped wound, indicating too that the bullet had ricocheted before striking Steinle.

Nonetheless, prosecutors have charged Lopez-Sanchez with intentionally firing at Steinle.

Lopez-Sanchez told police he fired the fatal bullet but called the incident an accident, according to his lawyer Matt Gonzalez and court testimony.

Lopez-Sanchez said he found the gun wrapped in a T-shirt under a bench on San Francisco’s Pier 14. The gun belonged to a Bureau of Land Management ranger, who had reported that his service weapon was stolen from his car in downtown San Francisco in June.

Divers plucked the gun from San Francisco Bay next to the pier the day after the shooting.

San Francisco Police ballistics expert Andy Smith testified that the gun was in good, working condition and that the weapon probably didn’t malfunction.

“Pulling the trigger, however that trigger was pulled, was the only way for that gun to discharge,” Smith said. “This gun could not just be sitting on a table and all of a sudden, due to some malfunction, go off.”

Gonzalez suggested that his client “mishandled” the gun, which needs about five pounds of pressure to pull the trigger and successfully fire.

Gonzalez said he plans to call a gun expert to the witness stand Thursday to testify about accidental shootings involving the gun Lopez-Sanchez fired.

San Francisco and other cities and counties ignore requests from federal authorities to detain jail inmates who are thought to be in the country illegally.

San Francisco Sheriff Ross Mirkarimi said he was following city law when jailers released Lopez-Sanchez after a 20-year-old marijuana possession charge was dropped. But leading politicians, including top Democrats such as California Sen. Dianne Feinstein and presidential hopeful Hillary Clinton, say Lopez-Sanchez should have been detained.