CHICAGO (STMW) — Four Chicago police officers were among nine people injured when an unmarked squad car was involved in a crash with two other vehicles on the Far South Side.

CBS 2’s Susanna Song reports the crash happened around 12:30 a.m. Monday, in the 10200 block of South Indianapolis Avenue.

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An unmarked Chicago police squad car pulled over a Chevy Tahoe for a traffic stop, and its emergency lights were flashing, and a second police car had pulled up in front of the Tahoe to assist. A Nissan Altima headed south on Indianapolis slammed into the unmarked squad car, which then crashed into the Tahoe, which rear-ended the second police car.

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“It sounded real loud. It sounded like a major crash, like a car pileup. … I just saw three cars; two squad cars, and a car that was pulled over. Like I said, they pulled the police officers out of the car. They fell to the ground, laid there. A lot of the victims, they couldn’t move; police officers couldn’t move,” said witness Met Gonzalez.

Of the nine people hurt in the crash, two were taken to John H. Stroger Jr. Hospital of Cook County, one person was taken to Advocate Christ Medical Center in Oak Lawn, one person was taken to Advocate Trinity Hospital, four people were taken to Roseland Community Hospital, and one person refused treatment, according to the Fire Department. All of the victims were in stable condition.

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The driver of the Altima was taken into police custody. As of 6:30 a.m., investigators have not determined if drugs or alcohol were a factor in the crash.