UPDATED 03/21/12 11:14 a.m.

CHICAGO (CBS) — An off-duty Chicago Police detective says he was just trying to quiet a crowd on the city’s West Side, when someone pulled a gun on him and left him with no choice to fire back.

As CBS 2’s Susanna Song reports, a 22-year-old woman and a 29-year-old man were still recovering from gunshot wounds as of 11 a.m.

LISTEN: WBBM Newsradio’s Bernie Tafoya reports

The woman was reported shot in the head, and was brought to Mount Sinai Hospital in an unknown condition. The man was shot in the hand, and was hospitalized at the same institution in good condition.

As of 11 a.m., police remained on the scene of the shooting, on 15th Place just east of Kedzie Avenue in the North Lawndale neighborhood. Evidence technicians were collecting evidence and marking where shell casings were found on the street.

CBS 2 counted at least 15 casings.

Police said around 1 a.m., the off-duty detective was pulling out of an alley in his car, when he came across four people who were being loud and rowdy on the street.

Police say the detective rolled down the window of his vehicle to investigate, and saw a man approach him with a handgun, then allegedly point it at him.

“(He) rolls the window down and says, ‘Hey guys, keep the noise down.’ At that point, one of the offenders comes at him as he’s sitting in his car. The offender has a weapon in his hand. The officer announced he’s police – ‘Drop the gun! Police!’ The offender continues to advance on him,” Camden said. “At that point, the officer fires, in fear of his life.”

But one resident who was outside at the time claims he didn’t hear a disturbance, as police allege.

“I didn’t hear no disturbance. All that I heard was gunshots,” said witness Marshall Walker. “I thought, like I said, I thought they were shooting each other, and I found out it was a police officer; shot the young girl and her cousin – one in the hand, and they shot her in the head, and she was in critical condition.”

Walker said he kept his distance.

“I don’t get involved in nothing like that,” he said. “I just stay out of the way.”

The other two people in the group that was allegedly causing the disturbance ran off.

Detectives are probing the incident, along with investigators from the Independent Police Review Authority.

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