DENVER -

A funeral is scheduled Saturday for a Denver policewoman who was shot and killed at a city park where families had gathered for a free weekly jazz concert.

Denver police say 21-year-old Rollen Oliver has been arrested in the shooting death of a policewoman at a city park.

Police Chief Robert White said Monday that Rollen Oliver was arrested on suspicion of first-degree murder in the fatal shooting of 32-year-old Officer Celena Hollis on Sunday.

Hollis was a single mother and a former officer with the Detroit Police Department.

Police say she was trying to break up a fight at the City Park Jazz festival when she was shot in the head. She was in uniform and working off-duty.

White says investigators don't believe the shots were aimed at Hollis, but they're not sure.

Earlier, police said they arrested one man on a weapons charge but didn't believe he was involved in the officer's shooting. It wasn't immediately clear if that was Oliver or someone else.

The Denver Post said Hollis was president of the Denver Black Police Officer's Association.

"She was easy to get along with and always had a smile on her face and happy to approach each day," Lt. Ron Thomas, a board member of the association, told the Denver Post.