FERGUSON, Mo. (AP) — An angry crowd of a couple hundred people marched into a suburban St. Louis County police department Sunday morning, demanding answers a day after a police officer shot and killed an 18-year-old black man.

Some in the crowd taunted police with chants of "Don't shoot me" as they held up their hands while walking into the Ferguson Police Department building. Officers stood at the top of a staircase and stopped the crowd without using force.

A news conference was held simultaneously in a different building. There, St. Louis County Police Jon Belmar said the incident began when the officer encountered two men on the street near an apartment complex on Saturday afternoon in a predominantly black suburb a few miles north of downtown St. Louis.

Belmar said one of the men pushed the officer back into his squad car and the struggle began. Belmar said at least one shot was fired inside the police car.

The struggle spilled out into the street where the teenager was shot. Police have not disclosed his name, but family members say it was 18-year-old Michael Brown.

Shell casings found at the scene matched the officers' gun. Belmar said the teen was shot multiple times, but it wasn't yet known how many.

"It was more than just a couple," he said.

Belmar said the officer has been with the Ferguson Police Department for six years and that he wasn't aware of other issues involving the man. The officer has been placed on paid administrative leave.

The protesters chanted "We want answers" and "no justice, no peace," Sunday morning and some carried signs saying "stop police terrorism" and "disarm the police."

John Gaskin, a member of the St. Louis County NAACP, said Saturday the FBI should get involved "to protect the integrity of the investigation."

He alluded to the 2012 racially charged shooting of 17-year-old Trayvon Martin by a Florida neighborhood watch organizer who was subsequently acquitted of murder charges, as well as the New York man who died from a police chokehold after he was confronted for selling individual cigarettes.

"With the recent events of a young man killed by the police in New York City and with Trayvon Martin and with all the other African-American young men that have been killed by police officers ... this is a dire concern to the NAACP, especially our local organization," Gaskin said.

State Sen. Jamilah Nasheed, D-St. Louis, told the St. Louis Post-Dispatch that she would ask the U.S. Justice Department on Monday for a formal investigation.

Brown's grandmother, Desiree Harris, said she saw him running in her neighborhood Saturday afternoon. Just minutes later, she heard a commotion and went outside to check on it. She found Brown's body less than two blocks away.

"When I got up there, my grandson was lying on the pavement. I asked the police what happened. They didn't tell me nothing."

Harris said her grandson had recently graduated high school and was looking forward to the future.

"My grandson never even got into a fight," she said. "He was just looking forward to getting on with his life. He was on his way."

Brown's mother, Lesley McSpadden, had harsh words Saturday for authorities: "You're not God, you don't get to decide when you get to take somebody from here," she told KSDK.

___

Associated Press writer Maria Sudekum contributed from Kansas City, Missouri.