FERGUSON, USA (AFP) – The trooper put in charge of tamping swirling racial tensions in this St Louis suburb vowed Sunday to stay “as long as it takes,” after violence flared anew.

Captain Ron Johnson also apologized for a white police officer’s shooting of 18-year-old Michael Brown, which caused long-simmering tensions to spill over for more than a week since his death in Ferguson, home to a black majority.

A curfew ordered by Missouri Governor Jay Nixon is due to take effect for a second night Sunday, potentially setting the stage for further confrontations.

“I want to start off by talking to Mike Brown’s family. I want you to know my heart goes out to you, and I say that I’m sorry,” Johnson said to loud cheering and applause from a crowd of more than 1,300 people at Greater Grace Church in Ferguson.

“I will be here as long as it takes.”

Hundreds more people stood outside the church that was filled to capacity, where passing cars honked at length.

Young people who had gathered outside held their hands in the air, paying homage to what some witnesses said was Brown’s last gesture before being shot.

Johnson, who grew up in St Louis, also acknowledged the personal toll the violence has taken on him.

“The last 24 hours have been tough for me,” he said.

Amid the growing violence, the federal government has stepped up its involvement in the investigation.

Attorney General Eric Holder is due to brief President Barack Obama on the situation on Monday, AURN radio reported.

“Our immediate goal is to make sure that the residents of Ferguson are safe, that the looting stops, that the vandalism stops, that the people who are living in the community are confident that justice will be done,” Obama senior advisor Valerie Jarrett told AURN.

The US Justice Department announced that a federal medical examiner would carry out an autopsy on Brown’s body, citing the case’s “extraordinary circumstances.”

That would mark the third autopsy of Brown, as extraordinary precautions were being taken in the sensitive investigation.

Federal investigators will take into account the autopsy performed by state medical examiners, a Justice Department spokesman said.

Brown’s family has also ordered an autopsy by famed forensic pathologist Michael Baden, who has testified at the trial of OJ Simpson, and was consulted for investigations into the deaths of John F. Kennedy and actor John Belushi.

Tensions flared anew overnight Saturday as police confronted around 200 protesters who defied a curfew.

Police used smoke bombs and tear gas to disperse demonstrators, while in a separate incident a woman was left fighting for her life after being shot.

Brown’s death at the hands of a white police officer has reignited a national debate about law enforcement and African Americans.

The Ferguson police force’s muscular response also drew criticism after officers were seen facing down protesters in military-grade armored trucks while toting high-powered assault rifles.

Johnson stressed why resolving the unrest in Ferguson was important to him and other black families.

“When this is over, I’m going to go in my son’s room, my black son, who wears his pants sagging, wears his hat cocked to the side, has tattoos on his arms, but that’s my baby,” he said.

“And we all ought to be thanking the Browns for Michael, because Michael is going to make it better for our sons, so they can be better black men. So they can be better for our daughters, so they can be better black women.”

A manager of a special needs institution who gave her name as Angel said there would only be peace in the community once citizens feel safe and have made peace with the police, who she said must be held accountable for what happened.

“Now that St Louis is standing up and people across the nation are standing up, I think it’s noticeable that people are not going to allow things like this to continue to happen, they are going to stand for things,” she told AFP.

Social worker Tia Mannierre stressed that “injustice is a big problem in a community.”

“We really have to set an example for the youth, we really have to do better for the community to come together and just make sure that these officers are held accountable for their actions because it’s not okay for you to just shoot someone in cold blood for absolutely no reason at all,” she said.

Brown’s family has accused authorities of a “devious” attempt to smear their son’s character after police named him as a suspect in the robbery of a Ferguson convenience store and released a surveillance video of the incident.

Police said the officer, unaware of the robbery, stopped the teen merely for walking in the middle of the street.

The Brown family’s attorney, civil rights lawyer Ben Crump, called Brown’s death an “execution.”

“When you put your hand up in the air, this means surrender. Don’t shoot,” said Crump, who represented the family of Trayvon Martin, an unarmed 16-year-old black teenager shot to death in Florida in 2012.