Speeding is "a way of life" at the San Antonio Police Department, former Officer David Seaton told jurors Tuesday, testifying at his manslaughter and aggravated assault trial.

"I know everybody in the courtroom here has had to have seen officers speeding. It's not new," Seaton said. "There was a lot of terrain to cover (in the West Side district) and I couldn't do it - I don't think anybody could do it - without speeding."

But that doesn't mean he sped through red lights, he added.

"That's basically suicide," Seaton said. "That doesn't make sense."

Seaton, 45, could face up to life in prison if jurors in the 226th state District Court agree with prosecutors that he was acting recklessly on Nov. 28, 2008, when he killed colleague Robert Davis while speeding through a red light at Potranco Road and Hunt Lane.

An in-car GPS system recorded Seaton driving 102 mph to a non-emergency shoplifting call just before he hit and severely injured motorist Darrell Lampkin at the intersection. Seaton's car then hit and pinned Davis, who was picking up flares along Potranco from a previous wreck.

Seaton told jurors repeatedly Tuesday that he has no recollection of the wreck or the events leading up to it. He remembered roll call that day and getting into a patrol car that wasn't his usual vehicle. His next coherent memory, he said, was waking up a week later at Wilford Hall Medical Center.

"I basically opened my eyes and said, 'Why am I here? What happened?'" he said. It would be days later before he was told about Davis' death, he said, describing the revelation as "a nightmare."

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"That was a tragic thing," Seaton said. "I felt very sorry, deeply sorry about what happened. My whole life is to basically preserve life and save lives."

Seaton estimated he handled 13 to 15 calls per shift in a district that could take 20 minutes to drive across. He kept personal records of more than 4,000 calls he responded to over the two years he was with the department. He would complain to supervisors about other officers who "sat" on calls for hours at a time, he said.

But prosecutor Charles Rich mentioned other records that he said showed Seaton travelling at speeds up to 100 mph on a somewhat regular basis. Less than an hour before the fatal wreck, GPS recorded him driving upwards of 80 mph along Potranco Road, Rich said.

Seaton responded that he didn't trust GPS devices. It would be "ridiculous" to say he travelled that fast every day, he said. But speed was sometimes necessary to back up other officers, he said.

"What am I going to do?" Seaton asked. "We're understaffed. We're undermanned. What kind of position have I been put in? There's no answer on how to fix it."

During his previous career as a firefighter in the military, he had additional training on driving vehicles at high speed, defense attorney Carolyn Wentland pointed out.

Testimony for Seaton's trial began last week and is expected to conclude Wednesday , after the defense calls three more officers. Among them is expected to be Sgt. Gabe Trevino, a former department spokesman who was involved in an unrelated fatal accident.