FERGUSON, Mo. (AP) — A Missouri teenager fatally shot by police suffered a bullet wound to his right arm that may indicate his hands were up or his back was turned to the shooter, but “we don’t know,” a pathologist hired by the teen’s family said Monday.

An independent autopsy determined that 18-year-old Michael Brown was shot at least six times, including twice in the head, according to the family’s attorneys and hired pathologists. Brown was unarmed when he was shot by a police officer Aug. 9 in Ferguson, touching off a week of rancorous protests in the St. Louis suburb. Police have used riot gear and tear gas, and the governor called in the National Guard early Monday to help.

Forensic pathologist Shawn Parcells, who assisted former New York City chief medical examiner Dr. Michael Baden during the private autopsy, said a bullet graze wound on Brown’s right arm could have occurred in several ways. He said the teen may have had his back to the shooter, or he could have been facing the shooter with his hands above his head or in a defensive position.

“We don’t know,” Parcells said. “We still have to look at the other (elements) of this investigation before we start piecing things together.”

Witnesses have said Brown had his hands raised above his head when he was repeatedly shot in a street in Ferguson, where the death has heightened racial tensions between the predominantly black community and the mostly white police department.

Another protest quickly deteriorated Sunday night as marchers pushed toward one end of a street, and authorities — who said they were responding to reports of gunfire, looting, vandalism and protesters who hurled Molotov cocktails — pushed them back with tear gas.

The streets were empty before a state-imposed midnight curfew, but hours later, Gov. Jay Nixon ordered the National Guard to Ferguson. It was unclear when the troops may arrive.

“These violent acts are a disservice to the family of Michael Brown and his memory and to the people of this community who yearn for justice to be served and to feel safe in their own homes,” Nixon said in a statement.

A grand jury could begin hearing evidence Wednesday to determine whether the officer, Darren Wilson, should be charged in Brown’s death, but it’s unclear how long it may take, said Ed Magee, spokesman for St. Louis County’s prosecuting attorney.

Family attorney Benjamin Crump said Brown’s parents wanted the additional autopsy because they feared results of the county’s examination could be biased. Crump declined to release copies of the report, and the county’s autopsy report has not been released.

“They could not trust what was going to be put in the reports about the tragic execution of their child,” he said during Monday’s news conference with Parcells and Baden, who has testified in several high-profile cases, including the O.J. Simpson murder trial.

The second autopsy, Crump said, “verifies that the witness accounts were true: that he was shot multiple times.”

Baden said one of the bullets entered the top of Brown’s skull, suggesting his head was bent forward when he suffered that fatal injury. The pathologists said Brown, who also was shot four times in the right arm, could have survived the other bullet wounds.

Baden also said there was no gun-power residue on Brown’s body, indicating he was not shot at close range. However, Baden said he did not have access to Brown’s clothing, and that it was possible the residue could be on the clothing.

Crump also noted that Brown had abrasions on his face from where he fell to the ground, but there was “otherwise no evidence of a struggle.”