Aiyana Stanley-Jones Update: Joseph Weekley, Detroit cop, testifies he didn't intend to kill 7-year-old

(CBS/AP) DETROIT - Joseph Weekley, a Detroit police officer charged in the fatal shooting of 7-year-old Aiyana Stanley-Jones, testified Thursday that he still feels "devastated and depressed" by what happened but wouldn't have acted differently during a hectic search for a murder suspect.

PICTURES: Aiyana Jones, 7, Killed by Cop

Weekley, who is charged with involuntary manslaughter, said he didn't immediately realize that he had shot Aiyana during the 2010 house raid. He said he unintentionally pulled the trigger when the victim's grandmother knocked his submachine gun.

"She hit it in a downward motion," Weekley told the jury. "As she hits it down, I start to pull it back. I hear the shot."

Nonetheless, Weekley said he believed the shot came from someone else in the house. He said he didn't even feel a recoil in the weapon.

Weekley, a member of an elite police unit, is accused of failing to control his gun. Defense attorney Steve Fishman said it simply was a tragic accident, not a crime. Aiyana's grandmother, Mertilla Jones, denies that she struggled for the gun, but the officer insists that's what happened.

Weekley said he wasn't reckless. But on cross-examination, he conceded: "If I fail to do ordinary care, that would be my fault."

He turned toward the jury as he explained what happened in the wee hours on Lillibridge Street in Detroit, even crouching on the floor to demonstrate his position before rushing through the door. Weekley kept his emotions in check, except for a brief moment when his attorney asked the officer about his two daughters, who were close in age to Aiyana.

Weekley paused, looked at the ceiling and ran his tongue under his lower lip. He had been with them at a park when he got a call to report to duty on a spring Saturday, hours before the fatal raid.

"I just feel devastated and depressed," Weekley said of the shooting. "I'll never be the same, no."

A stun grenade, which emits smoke, a bright light and vibrations, was thrown through a window before Weekley's Special Response Team entered the home. The raid was recorded for a police reality TV show, "The First 48," and some video was used at trial.

Complete coverage of Aiyana Stanley-Jones on Crimesider