FERGUSON, Mo. (AP) — Attorneys for Michael Brown's family vowed Tuesday to push for federal charges against the Ferguson police officer who killed the unarmed 18-year-old, and they renewed calls for peace following a night of violent protests in which several businesses burned to the ground.

The attorneys said the grand jury process was rigged from the start to clear the white officer, Darren Wilson, in the Aug. 9 shooting death of Brown, who was black. They criticized everything from the evidence St. Louis County Prosecutor Bob McCulloch presented to the jury to the way it was presented, as well as the timing of announcement of the grand jury's decision.

They said they still hope a federal civil rights investigation will result in charges against Wilson.

"We said from the very beginning that the decision of this grand jury was going to be the direct reflection of the presentation of the evidence by the prosecutor's office," said attorney Anthony Gray, who suggested McCulloch presented some testimony, including from witnesses who did not see the shooting, to discredit the process.

Meanwhile, Gov. Jay Nixon ordered hundreds more National Guardsmen into Ferguson to help local law enforcement keep order in the St. Louis suburb. Twelve commercial buildings in Ferguson burned down during protests that erupted after the grand jury's decision was announced Monday night, and firefighters responded to blazes at eight others, Assistant Fire Chief Steve Fair said. Other businesses were looted, and 12 vehicles were torched.

There were 61 arrests in Ferguson overnight, many for burglary and trespassing, and 21 in St. Louis, where protesters broke some store windows along South Grand Avenue.

At least 18 people were injured and sought treatment at area hospitals, including someone who was shot and was recovering Tuesday at SSM DePaul Health Center. The hospital didn't give any details about the shooting.

Brown's parents made public calls for peace in the run-up to Monday's announcement, and on Tuesday, their representatives again stressed that those setting fires and engaging in violence were not on Michael Brown's side.

Several daytime protests took place Tuesday. In Clayton, where the grand jury met, clergy members and others blocked morning traffic for several hours. In downtown St. Louis, where demonstrators swarmed the steps of a federal courthouse and stopped traffic, at least four people were arrested.

Many area districts canceled classes out of concern for the safety of students traveling to and from school.

The grand jury's decision means Wilson will not face any state criminal charges for killing Brown, whose death inflamed deep racial tensions between many black Americans and police.

Attorneys for Brown's family said they hope an ongoing federal civil rights investigation will lead to charges. For that to happen, though, investigators would need to satisfy a rigorous standard of proof in order to mount a prosecution. The department also has launched a broad probe into the Ferguson Police Department, looking for patterns of discrimination.

Regardless of the outcome of those investigations, Brown's family also could file a wrongful-death lawsuit against Wilson.

Wilson's lawyers issued a statement praising the decision and saying the officer, who has remained out of the public eye since the shooting but gave an interview that was to air on ABC Tuesday evening, is grateful to his supporters.

"Law enforcement personnel must frequently make split-second and difficult decisions," the lawyers wrote. "Officer Wilson followed his training and followed the law."

McCulloch, seeming defensive, spoke for 45 minutes Monday while explaining the grand jury's decision. He said the jury of nine whites and three blacks met on 25 separate days over three months and heard more than 70 hours of testimony from about 60 witnesses, including three medical examiners and experts on blood, toxicology and firearms. He repeatedly cited what he said were inconsistencies and erroneous witness accounts, and he never once mentioned that Brown was unarmed.

The protests that followed became quickly chaotic, with protesters looting and setting fire to businesses and vehicles, including at least two police cars. Officers eventually lobbed tear gas from inside armored vehicles to disperse crowds.

Shortly after the announcement, authorities released more than 1,000 pages of grand jury documents, including Wilson's testimony.

Wilson told jurors he initially encountered Brown and a friend walking in a street and, when he told them to move to a sidewalk, Brown responded with an expletive. Wilson then noticed that Brown had a handful of cigars, "and that's when it clicked for me," he said, referring to a radio report minutes earlier of a robbery at a nearby convenience store.

Wilson said he asked a dispatcher to send additional police, and then backed his vehicle up in front of Brown and his friend. As he tried to open the door, Wilson said Brown slammed it back shut.

The officer said he pushed Brown with the door and Brown hit him in the face, leading him to draw his gun and threaten to shoot Brown. He said Brown grabbed the gun and, fearing for his life, he fired it. Brown then fled and Wilson gave chase. At some point, Brown turned around to face the officer.

Witness accounts were conflicted about whether Brown walked, stumbled or charged back toward Wilson before he was fatally wounded, McCulloch said. There were also differing accounts of how or whether Brown's hands were raised. His body fell about 153 feet from Wilson's vehicle.

The August shooting heightened tensions in the predominantly black suburb patrolled by an overwhelmingly white police force. As Brown's body lay for hours in the center of a residential street, an angry crowd of onlookers gathered. Rioting and looting occurred the following night, and police responded with armored vehicles and tear gas.

Protests continued for weeks — often peacefully, but sometimes turning violent, with demonstrators throwing rocks and Molotov cocktails and police firing smoke canisters, tear gas and rubber bullets. Nixon briefly summoned the National Guard.

Ashon Bumaka, 46, of nearby Black Jack, surveyed the damage Tuesday morning.

"As you can see, it's sad man ... this don't look like a city in the United States. Right now this looks like some foreign area that the government has betrayed the people."

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Link to grand jury documents: http://hosted.ap.org/specials/interactives/_documents/ferguson-shooting/ .

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Associated Press writers Alan Scher Zagier in Clayton, Andale Gross and Jim Suhr in Ferguson and Catherine Lucey in Des Moines, Iowa, contributed to this report. Follow David A. Lieb at: https://twitter.com/DavidALieb .