ANN ARBOR, MI - Police determined an Ann Arbor police officer was at fault in a three-vehicle rollover crash last week.

Ann Arbor police Sgt. William Clock said the officer, who has not been identified yet, was at fault in the May 12 incident at Huron Street and Fourth Avenue in downtown Ann Arbor.

Police previously said the officer was headed eastbound on Huron Street at about 5:30 p.m. Thursday when he struck a southbound white Ford Escape at the Fourth Avenue intersection. The collision caused the Escape to roll on top of another vehicle.

Although no one was reported to have been seriously injured and no one was transported by Huron Valley Ambulance, the officer was taken to an area hospital as a precaution, police said.

Clock declined to comment further on the incident and Ann Arbor Police Chief Jim Baird did not immediately respond to requests for comment. However, two witnesses said they believe the officer was on his cellphone and had a red light at the time of the crash.

Todd Wilson, 35, of Saline said he was waiting at a red light westbound on Huron Street when he saw the crash out of the corner of his eye.

"I looked up as (the officer was) skidding, hitting the car," he said. "I'm certain the light was still red ... It kind of looked like he rolled through the red light, trying to turn or wasn't paying attention."

The officer had a phone in his hand, Wilson said. He struck a white Ford Escape, causing it to tip on top of another vehicle.

Katherine Mays, 26, of Ann Arbor was walking north across Huron Street in the crosswalk to go to a meeting when the crash occurred, she said.

She said she noticed the police vehicle in the far right lane of eastbound Huron Street before she began to cross the street. She did not notice any turn signals and did not see the vehicle's lights or sirens running.

Shortly after, she heard the crash, turned around and saw the officer pulling a cellphone from his face, she said.

"My immediate thought was 'Oh my God, that cop is talking on his cellphone,'" she said. "He was not picking it up, he was putting it down."

Both Wilson and Mays said onlookers began to yell that the officer was on his phone, as well.

Talking on a cellphone while driving is not specifically prohibited by Michigan law, but a motorist who commits a traffic violation while talking on a cellphone may be charged with careless driving, according to the Michigan State Police.

Wilson said the officer was a bit slow to get out of his vehicle, but Mays said he checked on the other drivers.

Although Wilson kept driving as soon as traffic cleared, he said he believes the driver of the vehicle underneath the Escape, a Buick Encore, may have tried to pull his vehicle forward. He heard onlookers yelling for him to stop.

Mays, who stopped to give a report to police, said she believes the driver was trying to get out of his vehicle by opening the door the Escape was pressed against.

Both witnesses said the officer should receive the same consequences as any other driver.

"The way this happened, it could have killed someone," Mays said.

The Ann Arbor News has requested the police report on the crash through the Freedom of Information Act.

Darcie Moran covers cops and courts for MLive and The Ann Arbor News. Email her at dmoran@mlive.com or follow her on Twitter @darciegmoran.