Gov. Jay Nixon ordered the Missouri National Guard to begin withdrawing from this St. Louis suburb Thursday, the clearest sign yet that the violent clashes between police and residents may be subsiding after nearly two weeks of civil unrest.

Nixon’s decision came four days after he first called on Guard troops to help contain the escalating protests over the police shooting of 18-year-old Michael Brown on Aug. 9. The nightly confrontations between protesters and a heavily armed police force wielding tear gas canisters and rubber bullets have attracted global attention.

In a statement, Nixon (D) said the security situation in Ferguson had improved, after a night when just six people were arrested, far fewer than in previous nights. In total, at least 161 people have been arrested in disturbances linked to Brown’s shooting.

The signs of easing tensions came as a family friend of the officer who fatally shot Brown came forward to offer a version of the incident with new details, saying that the officer suffered a fracture to his eye socket in a scuffle with the unarmed teenager before opening fire.

Hospital X-rays of the injury have been taken and will be shared with a grand jury that is weighing evidence to determine whether Officer Darren Wilson should be charged in the shooting, said the friend, who spoke on the condition of anonymity because of fear of threats. The friend has been in contact with Wilson’s family members.

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Ed Magee, a spokesman for St. Louis County Prosecutor Robert McCulloch, declined to comment on the new reports about Wilson, and said prosecutors have not received any medical records. But he said that because Wilson was taken to the hospital, McCulloch’s office assumes such records exist.

McCulloch has been in touch with Wilson’s attorney, but has not spoken to Wilson, Magee added. Wilson will be given an opportunity to appear before the grand jury, but he cannot be compelled to appear.

Prosecutors began presenting evidence to the St. Louis County grand jury Wednesday. McCulloch has said that it could be mid-October before all the evidence is presented, noting that not all of it is ready yet.

Meantime, on Capitol Hill, Sen. Claire McCaskill (D-Mo.) said Thursday she will hold a hearing in September to examine the militarization of local police departments. Authorities in Ferguson and St. Louis County have been criticized for deploying heavy militarized equipment to help quell the protests.

Since Brown was killed, authorities have provided relatively few details about the encounter between the teenager and Wilson. Ferguson Police Chief Thomas Jackson said last week that Wilson had a “swollen face” after the altercation and was taken to a hospital for treatment, but he did not provide any other information beyond saying the injuries were not life-threatening.

A day after Brown was shot, St. Louis County Police Chief Jon Bellmar told reporters that Brown “allegedly pushed” Wilson back into the car and physically assaulted him. Bellmar did not elaborate.

Dorian Johnson, 22, who was with Brown and said he witnessed the shooting, has said that Wilson instigated the confrontation, pulling up to the pair in his police cruiser and telling them to get out of the middle of the street.

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Freeman Bosley Jr., Johnson’s attorney and a former St. Louis mayor, told The Washington Post that Wilson pulled up so close to Brown that when he opened his car door, it bumped into the teenager.

Wilson reached out and grabbed Brown by the throat and grabbed his shirt as Brown tried to move away, Bosley said. At that point, Johnson said he saw Wilson pull out a gun and shoot Brown in the chest or arm. Johnson said the officer hit Brown with another round as he was running away and fatally gunned him down after he stopped and raised his hands in surrender.

Michael Brady, another eyewitness, told CNN that he saw “some kind of tussle going on” with Wilson still inside the car and Brown next to it. Brady said Brown and Johnson then ran away, while Wilson got out of his car and began shooting.

A private autopsy showed that Brown had at least six gunshot wounds and that all of the rounds were fired from the front, none of them at close range.

Wilson, 28, who is now in a secret location and under police protection because of death threats, has told family and friends that he knows he was justified in the Aug. 9 shooting but is “brokenhearted” about having taken a life in the line of duty, the friend said.

In his account to close confidants, Wilson has repeatedly said he thought Brown was acting erratically when they had an altercation on a street in a garden apartment complex in Ferguson. He said that Brown was coming at him when he fired the fatal shots.

“Darren was adamant that he believed Michael Brown had some drugs in his system,” the friend said.

Preliminary results of a county autopsy showed that Brown had marijuana in his system. Full toxicology tests of Brown’s blood have not been completed, the friend said, and the family is awaiting that information.

In Washington, Attorney General Eric H. Holder Jr. reiterated a pledge Thursday that the Justice Department would conduct a “thorough and fair” investigation into the shooting of Brown. He spoke a day after he visited Ferguson for meetings with elected officials, community leaders and members of Brown’s family.

“My commitment to them is, long after this tragic story no longer receives this level of attention, the Justice Department will continue to stand with Ferguson,” Holder added.

Branigin reported from Washington. David Nakamura and Mark Berman in Washington contributed to this report.