Updated

A Detroit police officer charged in the fatal shooting of a 7-year-old girl testified Thursday that he's trained to keep his finger off the trigger, but he insisted the split-second tragedy began when the victim's grandmother grabbed his weapon during a risky midnight raid.

Joseph Weekley, charged with involuntary manslaughter, testified in his own defense on the eighth day of trial, telling jurors that he remains "devastated and depressed" over the death of Aiyana Stanley-Jones, who was shot in the head while she slept on a couch in May 2010.

"I was pretty messed up at the time. I shot a kid. ... To be involved, even to this day, you can't explain it. It's horrible," Weekley said.

He was the first officer in as police raided a house to round up a man suspecting of killing a teenager outside a corner store less than 48 hours earlier. A stun grenade was thrown through a window, emitting smoke, bright light and vibrations intended to confuse people.

Weekley said he heard a noise from under a pile of laundry and blankets on a couch near the doorway. He said a woman later identified as Aiyana's grandmother, Mertilla Jones, emerged.

"She hit it in a downward motion," Weekley said of his submachine gun. "As she hits it down, I start to pull it back. I hear the shot."

Nonetheless, he said he didn't even feel a recoil in the weapon and first believed the shot came from elsewhere in the house.

Later in closing arguments, prosecutor Rob Moran said Weekley's version doesn't make sense. He said Jones would have had to rise from the couch after the grenade was detonated and interfere with the officer in just seconds.

"It didn't happen," Moran said. "It did not happen."

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.

The jury will have three options Friday: involuntary manslaughter, a felony; a misdemeanor weapons charge; or not guilty of any crime.

"All he had to do was keep his finger off the trigger," Moran said.

"He may be a good police officer. He may be a good father. He may be a good person," the prosecutor said of Weekley. "It does not matter. ...  Because of his conduct, Aiyana Jones is dead."

Fishman told jurors that Mertilla Jones' denial of any struggle with Weekley has no credibility. He reminded them that Aiyana's grandmother had accused police of intentionally killing the girl.

"Joe Weekley was not careless, reckless or negligent," Fishman said.

Weekley turned toward the jury as he explained what happened in the wee hours on Lillibridge Street, 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.

He paused, looked at the ceiling, took a deep breath and ran his tongue back and forth 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."

The raid was recorded for a police reality TV show, "The First 48," and some video was used at trial.