Defense attorneys for ex-Minneapolis police officer Mohamed Noor have argued he shot 911 caller Justine Ruszczyk in an alley after she slapped the back of his police squad as she approached, startling him and his partner and leaving them fearing for their lives.

But an expert testified Monday that Ruszczyk's fingerprints were not found on the squad.

Jennifer Kostroski, a forensic scientist with the Minnesota Bureau of Criminal Apprehension, told the court she could not conclude if Ruszczyk touched the squad, and there was nothing on the back of the vehicle that required further analysis.

Under cross examination, defense attorney Thomas Plunkett introduced the possibility the car might have been touched with a closed fist or in a "back-handed slap" manner. He asked Kostroski whether knuckles would leave latent prints. She said no.

The question of whether or not Ruszczyk slapped the squad car before she was fatally shot has become a key question at Noor's trial and a key part of his defense against murder and manslaughter charges he faces for the July 2017 shooting.

Minneapolis police officer Matthew Harrity testified Thursday he heard a "thump" and a "murmur" in the alley and worried of a possible ambush before his partner, officer Mohamed Noor, shot and killed 911 caller Justine Ruszczyk. Cedric Hohnstadt for MPR News

Officer Matthew Harrity, Noor's former partner, testified last week that he heard a thump and the noise startled and terrified him.

Prosecutors have argued that police officers at the crime scene concocted the story of a noise, and that Harrity didn't mention it to investigators until three days after the shooting.

On Monday, Chris Olson, a special agent in charge at the BCA, testified that he was frustrated that there didn't seem to be much information about what happened at the crime scene.

Olson said Sgt. Shannon Barnette told him that it sounded like Ruszczyk "made contact with the car." He said he asked what sort of contact, and Barenette replied that it was a "slap."

Former Minneapolis police officer Mohamed Noor (second from left) during his trial on Wednesday, April 10, 2019. Cedric Hohnstadt for MPR News

Olson said he passed information about the sound to another BCA agent who wrote the search warrants that prosecutors said were the first official filings to describe a noise before the shooting.

A BCA search warrant on the morning after the shooting made the first mention of a "slap" on a car. Most officers interviewed in the trial have said they didn't hear about a noise on the squad at the crime scene.

Prosecutor Patrick Lofton has argued in court that a Minneapolis police sergeant talking to a BCA agent at the crime scene suggested that maybe the car was slapped.

Eric Knutson, the BCA agent who initially oversaw the crime scene, told the court Monday that one of the other BCA agents told him at the scene that the squad was slapped, but he couldn't remember who it was.

Noor is charged with second- and third-degree murder and second-degree manslaughter in the killing of Ruszczyk, also known as Justine Damond, in July 2017.

She had called 911 to report what she thought was an assault happening behind her home. Investigators say Noor, one of the responding police officers, shot Ruszczyk through the open driver's side window of the squad in an alley near her home.

Noor's defense attorneys have argued the officer fired to protect his terrified partner after hearing a thump on the squad and then seeing a figure by the driver's side window raise their right arm.

Prosecutors say the thump was a story made up later and that Ruszczyk, who was in her pajamas as she approached the squad, could not have been considered a threat.

The BCA typically handles police shooting investigations in Minnesota, but its work has come under scrutiny in this case.

MPD Deputy Chief Kathy Waite testified at Noor's trial last week that she disagreed with how the BCA collected evidence on the squad vehicle at the crime scene.

She said the agency should have taken the vehicle somewhere to be analyzed. Waite also said that Ruszczyk's body should not have been left on the ground for as long as it was.

Attorneys are also exploring why the state agency returned the squad car to Minneapolis police so quickly when they knew the shot was fired from inside it.

Barnette then ordered the car to be washed and returned to service, although it was later sent back to the BCA for additional testing.

April 16: Prosecution raps police supervisor who shut off bodycam

Minneapolis Officer Jeremy Foster testified Monday that he was told to bring the squad from the MPD to the BCA parking garage on July 20, but not warned to wear gloves or preserve evidence in the vehicle.

He said there was a sign in the squad window that said "something like keep out or don't use."