A man was stabbed to death on LaSalle Street in the River North neighborhood just before 4 a.m. Saturday, according to police.

The man, identified by police as Eric Lopez, was attacked by a group of people after exchanging words with them at a nearby BP gas station at the corner of Ontario Street and LaSalle Boulevard, according to a security guard at the gas station.

He and another man were stabbed at about 3:45 a.m. in the 600 block of North LaSalle Boulevard, said Chicago Police Department News Affairs Officer Jose Estrada.

The man killed suffered "several stab wounds to the chest," Estrada said. A 17-year-old boy who was wounded -- family said he had been stabbed in the knee -- has been released from the hospital as of early Saturday afternoon, said Estrada.

The 20-year-old Lopez was pronounced dead of apparent stab wounds at 4:18 a.m. at Northwestern Memorial Hospital, according to the Cook County Medical examiner's office. An autopsy is planned for Sunday.

The man who died was with a group of people in a silver minivan that tried to leave the gas station after an argument with three people on Ontario Street, said Brandon Bush, the BP security guard.

The group of three swelled to more than ten people, who chased the van after it pulled away, Bush said.

"The crowd grew to between ten and fifteen people and they were rushing the car," Bush said. "Two of them didn't make it in the car."

The van went north on LaSalle before doing a U-turn to double back and apparently get the two people who didn't make it in the van, Bush said. Meanwhile, the larger group was trying to hit people in the car, throwing bottles at it, and someone in the van was swinging a club at the group, Bush said.

The group got ahold of the man who died, who was found on the sidewalk in front of the south-facing minivan by responding police. Bush waited with the man as he died.

"I'm sitting there, trying to hold him," Bush said. "I never saw the weapon. They were stomping him. I thought he was shot because the puncture wounds were so deep.

"He was soaked in blood. It looked like they hit him in the head, it looked like they stomped him in the face."

The van was driven by an 18-year-old man who was out with two close friends and one woman, plus the man who was stabbed and the dead man's cousin, said the 18-year-old's mom, Mirabel Ayala.

Ayala had rushed to the area once she learned someone had been stabbed. Her son, his two friends and the woman were taken away by police for questioning, she said.

Police taped off the block between Ontario and Erie streets while detectives questioned Bush and others. The BP was also closed for business and the station's manager arrived before 6 a.m. It's not clear if police were able to get usable security footage from the gas station.

No arrests have been made and Area Central detectives are investigation, Estrada said.

Tribune reporter Rosemary R. Sobol contributed

pnickeas@tribune.com
Twitter: @peternickeas