PITTSBURGH — A white former police officer said Thursday he thought a weapon was pointed at him when he shot and killed an unarmed black teenager outside Pittsburgh last summer.

Former East Pittsburgh Police Officer Michael Rosfeld took the stand at his homicide trial and insisted he was in fear for his life when he gunned down 17-year-old Antwon Rose II.

Rosfeld, 30, got choked up and dabbed away tears as he recounted finding the mortally wounded Rose on the ground. “I was upset, shocked,” Rosfeld said. “He was moaning, trying to breathe.”

The former officer testified after the prosecution rested its case earlier Thursday. Prosecutors said Rosfeld gave inconsistent statements about the shooting, including whether he thought Rose had a gun.

A prosecution witness has said that after the shooting, he heard Rosfeld say repeatedly, “I don’t know why I shot him. I don’t know why I fired.” But another prosecution witness said he heard the officer ask, “Why did he do that? Why did he take that out of his pocket?”

Rosfeld fired three bullets into Rose after pulling over an unlicensed taxi he suspected — correctly, as it turned out — to have been involved in a drive-by shooting. Rose, a passenger in the car, was shot in the back as he fled.