CHICAGO (CBS) — Chicago police have released several people who were brought in for questioning after two officers were shot Tuesday night in the Back of the Yards neighborhood.

The officers were sitting in a surveillance van near 43rd and Ashland around 9:15 p.m. Tuesday, following up on the investigation of an earlier incident, when one or two vehicles pulled up and the people inside opened fire.

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Police said three people of interest were being questioned shortly after the shooting.

Chicago Police Department spokesman Anthony Guglielmi confirmed they have been released.

“We questioned multiple people in reference to the shooting and yes, they were released,” he said in an email Thursday morning.

Guglielmi said the investigation of the shooting is ongoing.

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The two officers who were shot were released from the hospital on Wednesday.

Police launched a massive manhunt after the shooting, and Police Supt. Eddie Johnson said he’s confident the shooters will be found.

“Make no mistake about it, we’re going to catch them. We are going to get these individuals responsible,” Johnson said.

Police have said investigators believe the shooters used a high-powered weapon when they opened fire on the two Deering District tactical officers. Police quickly located a silver minivan and a silver Trailblazer abandoned nearby, one with an automatic rifle inside.

Detectives also believe, although the officers were in plain clothes and driving an unmarked van, they appeared to have been followed and targeted.

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Johnson ordered “heightened security” for the two officers after they were released from the hospital.