FERGUSON/KANSAS CITY, Mo. - Police fired tear gas after rioting broke out for a second night in Ferguson, Missouri, despite calls on Monday for calm from the mother of a black teenager who was shot to death by police at the weekend.

Ferguson Police Chief Tom Jackson said officers were focused on dispersing the crowd, which was smaller than the night before, but were making arrests and reported being fired on at some locations.

"They are shooting at us now," Jackson said, adding that officers from 10 to 15 jurisdictions were assisting Ferguson.

Michael Brown, 18, was shot to death in Ferguson, a mostly black St Louis suburb, on Saturday afternoon after what police said was a struggle with a gun in a police car. The FBI has opened a probe into the racially charged case.

#Ferguson teen killed by police is remembered as “gentle giant” who didn’t cause trouble. http://t.co/Y440iNbQgupic.twitter.com/iIURiRkyD6 — Jim Roberts (@nycjim) August 11, 2014

Brown's family has hired Benjamin Crump, the attorney who represented the family of Trayvon Martin, a black teenager who was shot to death by a community watch volunteer in 2012.

Police in riot gear fired tear gas to disperse a crowd estimated in the hundreds gathered near a building that burned during Sunday night's rioting, he said.

Fire trucks, ambulances and more officers converged on the area in a chaotic scene. One officer in riot gear stood behind a squad car in a standoff with a group of young demonstrators.

Emergency services said they had responded to reports of a stabbing and a shooting, but had not confirmed such incidents and emergency workers were told later to pull back from the area.

A witness in the case told local media Brown had raised his arms to police to show he was unarmed before being killed.

"He just graduated and was on his way to college," said Brown's mother, Lesley McSpadden, speaking through tears at a news conference. She said her first-born son's first day back at school would have been Monday.

"We can't even celebrate," she said.

The FBI opened a federal inquiry into the case intended to supplement the main investigation by St. Louis County police, according to the U.S. Department of Justice.

It was not immediately clear from police why Brown was in the police car. At least one shot was fired during the struggle, and then the officer fired more shots before leaving the car, police said.

OFFICER NOT IDENTIFIED

The officer, who was not identified, is a six-year veteran and has been put on administrative leave, police said. The officer's race has not been disclosed.

Dorian Johnson told television station KMOV that he and Brown had been walking when an officer confronted them, drew a weapon and shot. Johnson said that Brown put his hands in the air and started to get down, but the officer kept shooting.

Jackson said there was plenty of physical evidence and witness testimony. "I really believe we can get to the truth of what happened here," he said.

Demonstrations to call for justice for Brown turned violent Sunday night. Crowds broke the windows of cars and stores, set a building on fire and looted shops. At least two dozen businesses were damaged, 32 people were arrested, and two officers injured.

"I think it is crazy. It's nonsense. What does it bring back? It's not going to bring the man back," said Adrian Brewer, 30, an African American from a city near Ferguson.

Hundreds of demonstrators had gathered earlier on Monday at the town's police station to demand that the officer responsible for Brown's death face murder charges. Police arrested up to 15 people during that mostly peaceful demonstration.

On Monday night, demonstrators driven out by tear gas gathered at the station, chanting "hands up, don't shoot."

Brown's mother said her son had been planning to study heating and air conditioning repair at a technical college.

Michael Brown Sr., the teen's father, told reporters his son was "silly" and "could make you laugh."

"We need justice for our son," he said.

Three of the Ferguson Police Department's 53 members are black, Jackson said. About two-thirds of Ferguson's population of about 21,000 are black, according to U.S. Census figures.

Ferguson's median household income is $37,517, less than the Missouri average of $47,333.

Most of the communities around Ferguson have gone from white to mostly black in the last 40 years, said Terry Jones, political science professor at University of Missouri-St. Louis.

"There's a long history of racial injustice," said Jones. "Slowly and not so surely, the St. Louis metropolitan area has been trying to figure out a way forward. As the Michael Brown shooting indicates, there are often setbacks."