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

The attorneys said the grand jury process was rigged from the start to clear Officer Darren Wilson in the Aug. 9 shooting death of Brown. And they criticized everything from the types of evidence St. Louis County Prosecutor Bob McCulloch presented to the jury to the way it was presented and the timing of the grand jury’s decision. They also said they hope that 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 more National Guardsmen into Ferguson to help local law enforcement keep order in the St. Louis suburb. Twelve commercial buildings in Ferguson were burned down during the 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 also 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.

Jon Belmar, chief of the St. Louis County police, said that unless his agency could bring in 10,000 officers, “I don’t think we can prevent folks who really are intent on destroying a community.”

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. Two other people were admitted to Barnes-Jewish Hospital for undisclosed injuries. Everyone else was treated and released.

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

There were several area protests on Tuesday, including one in Clayton, where the grand jury met, in which clergy members and others blocked traffic for several hours and another through downtown St. Louis in which protesters swarmed the steps of a federal courthouse and stopped traffic. Nobody was arrested at the Clayton protest and at least four people were arrested at the one in St. Louis.

Meanwhile, many area districts cancelled classes out of concern for the safety of students traveling to and from school.

The grand jury’s decision means that Wilson, who is white, will not face any state criminal charges for killing Brown, who was black and unarmed. Brown’s death inflamed deep racial tensions between many black Americans and police.

Attorneys for Brown’s family said they still hope that an ongoing federal civil rights investigation will lead to charges. For that to happen, 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 could also 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, 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 said the jury of nine whites and three blacks met on 25 separate days over three months, hearing more than 70 hours of testimony from about 60 witnesses, including three medical examiners and experts on blood, toxicology and firearms.

Speaking for nearly 45 minutes, a defensive McCulloch repeatedly cited what he said were inconsistencies and erroneous witness accounts. He never mentioned that Brown was unarmed.

As McCulloch read his statement, Michael Brown’s mother, Lesley McSpadden, sat atop a vehicle listening to a broadcast of the announcement. When she heard the decision, she burst into tears and began screaming before being whisked away by supporters. The crowd with her erupted in anger, converging on the barricade where police in riot gear were standing and pelting them with objects, including a bullhorn. The officers stood their ground.

The protest became more 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 that 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. Wilson told grand jurors he was thinking: “What do I do not to get beaten inside my car.”

“I drew my gun,” Wilson told the grand jury. “I said, ‘Get back or I’m going to shoot you.’”

“He immediately grabs my gun and says, ‘You are too much of a pussy to shoot me,’” Wilson told grand jurors. He said Brown grabbed the gun with his right hand, twisted it and “digs it into my hip.”

Asked why he felt the need to pull his gun, Wilson told grand jurors he was concerned another punch to his face could “knock me out or worse.”

After shots were fired in the vehicle, Brown 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 that is 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.

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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 .