FERGUSON, Mo. >> A Missouri teenager fatally shot by police suffered a bullet wound to his right arm that may have occurred when he put his hands up or while 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 conducted on 18-year-old Michael Brown determined that the teen was shot at least six times, including twice in the head, according to the hired pathologists and the family’s attorneys. Brown was shot by a police officer Aug. 9 in Ferguson, touching off a week of rancorous protests in the St. Louis suburb where police have used riot gear and tear gas.

Forensic pathologist Shawn Parcells, who assisted former New York City chief medical examiner Dr. Michael Baden during the autopsy, said a bullet graze wound on Brown’s right arm could have occurred in several ways. 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 across his face or chest, Parcells said.

“But we don’t know,” he added.

Witnesses have said Brown had his hands raised above his head when he was repeatedly shot in a street.

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.

Brown’s death heightened racial tensions between the predominantly black community and the mostly white Ferguson Police Department, leading to several run-ins between police and protesters. The governor has called in the National Guard to help and put the Missouri Highway Patrol in charge of security.

A grand jury could begin hearing evidence Wednesday to determine whether the officer, Darren Wilson, should be charged in Brown’s death. Prosecutors are expected to try to start presenting evidence in the regular once-a-week meeting day for the grand jury, though it’s unclear how long it may take, said Ed Magee, spokesman for St. Louis County’s prosecuting attorney.

Family attorney Benjamin Crump said the family wanted the additional autopsy because they feared results of the county’s examination could be biased. Crump declined to release copies of the report to the media, 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.”

He said Brown’s mother “had the question any mother would have: Was my child in pain. Dr. Baden shared with her in his opinion, he did not suffer.” 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.”

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Associated Press writer Jim Salter contributed to this report from St. Louis.