GARY, Ind. (CBS) — A person of interest arrested in the murder of a Gary police officer on Sunday remained in custody on Friday, but has yet to be charged.

WBBM Newsradio’s Mike Krauser reports, according to a source close to the investigation, detectives believe they have Officer Jeff Westerfield’s killer in custody, but don’t have enough evidence to file murder charges yet.

That would explain why the Lake County Sheriff’s office has offered a $10,000 reward for information leading to a prosecution.

Westerfield, a 19-year veteran of the Gary Police Department, was shot and killed in the driver’s seat of his patrol car at 26th Avenue and Van Buren Place while responding to a call of shots fired at that location on Sunday.

A person of interest in the shooting was taken into custody hours later, and authorities said at the time they were confident he was the right suspect.

Police can continue holding him without filing murder charges, because he is wanted on an unrelated arrest warrant in Porter County.

On Wednesday, before the reward was announced, more than 100 police officers – many of them volunteers – combed the area where the shooting occurred, to search for new evidence.

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