Police were coming up short Monday in their investigation of a mass shooting in Chicago's River North district, which killed one man and left three others in critical condition.

A $10,000 reward is now on the line from Cook County Crime Stoppers for information that leads to an arrest in the early Sunday morning shooting.

Chicago police Monday morning said they definitely need help from the public in their efforts to solve the murder. Details are sparse, and investigations were not able to provide a description of the shooters or of the getaway vehicle.

The shooting happened at 2:35 a.m. in the 400 block of North LaSalle Drive, near Hubbard Street.

Police said the victims were getting into a car when four unidentified suspects approached them on foot, pulled out guns, and opened fire.

A 34-year-old man suffered multiple gunshot wounds to his body and was taken to Northwestern Memorial Hospital, where he died.

A 36-year-old man was shot in the chest, a 43-year-old man was shot in the back, and a 35-year-old man suffered multiple gunshot wounds throughout his body. All were taken to Northwestern Memorial Hospital in critical condition.

Police said the armed suspects then got into a car and drove away from the scene. For most of the morning, police focused on a green Lamborghini, which was surrounded by evidence markers.

Witnesses said they heard 50 shots fired.

"I was actually asleep, and then I woke up to like the loud noises, and I didn't really know what was going on. I thought maybe it was gunshots, but then I don't know — I was really groggy," one woman said. "But then there was a like a little pause, and there was ton more, and I was like, oh gosh, that's not sounding great."

Police have not indicated whether the shooters and the victims knew each other, or if the shooting was a random act of violence.

Cook County Crime Stoppers announced Sunday that it is offering a $10,000 reward for information leading to an arrest in the ass shooting.