A white Alabama police officer charged with murder in the killing of a black man testified Thursday he is still remembering new details about the shooting nearly four years later.

The Montgomery Advertiser reported that Montgomery police Officer Aaron Cody Smith took the stand to testify about the slaying of 58-year-old Greg Gunn in February 2016.

Gunn was shot to death while walking in his own neighborhood around 3 a.m. On patrol, Smith saw Gunn and stopped him for questioning moments before the confrontation turned violent.

Prosecutors argue Smith has given differing accounts of the shooting, including varying on whether the man swung a pole at him before he began shooting.

Smith told his lawyer during testimony that his memory of the shooting has varied and he is still remembering new things.

“I don’t know exactly the way the anatomy of my brain works, but I was in a traumatic incident and it affected me immediately after the shooting,” Smith said. “I dream about it at night. I wake up, and it’s the first thing I think about in the morning when I wake up. As time goes on, new details come up.”

While prosecutors have questioned Smith’s legal right to stop Gunn, the officer said he stopped Gunn in an area where there had been a rash of break-ins.

“He was walking on the sidewalk and his actions threw up a red flag, he saw me and started walking quickly,” Smith said.

The trial was moved from Montgomery to the southeast Alabama town of Ozark, about 85 miles away, because of publicity in the capital.