Story highlights Protester in Ferguson says, "He should have been fired on Day One"

Wilson's resignation letter: "It is my hope that my resignation will allow the community to heal"

His lawyer tells CNN Wilson heard threats had been made against the police department

Wilson had been in hiding since the August slaying of Michael Brown in Ferguson, Missouri

Darren Wilson, the police officer who fatally shot an unarmed teenager in August, has resigned from the police department in Ferguson, Missouri, his attorney, Neil Bruntrager, confirmed to CNN Saturday night.

In a telephone interview with the St. Louis Post-Dispatch, Wilson said he resigned after the police department told him it received threats of violence if he remained an employee.

"I'm resigning of my own free will," he said. "I'm not willing to let someone else get hurt because of me."

He said resigning was "the hardest thing I've ever had to do."

The resignation, which is immediate, comes five days after a grand jury decided not to indict Wilson in the killing of Michael Brown, 18.

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Photos: Unrest in Ferguson Photos: Unrest in Ferguson Police officers walk past the smoldering remains of a beauty supply store in Ferguson, Missouri, on Tuesday, November 25. Ferguson has been struggling to return to normal since Michael Brown, an unarmed black teenager, was killed by Darren Wilson, a white police officer, on August 9. The grand jury did not indict Wilson in the case, prompting new waves of protests in Ferguson and across the country. Hide Caption 1 of 34 Photos: Unrest in Ferguson A woman cleans up glass from a business' shattered window on November 25. Hide Caption 2 of 34 Photos: Unrest in Ferguson A Ferguson firefighter surveys rubble at a strip mall that was set on fire overnight. Hide Caption 3 of 34 Photos: Unrest in Ferguson Protesters run away after police deployed tear gas in Ferguson on Monday, November 24. Hide Caption 4 of 34 Photos: Unrest in Ferguson Police take position during clashes with protesters on November 24. Hide Caption 5 of 34 Photos: Unrest in Ferguson A protester stands in front of police vehicles with his hands up on November 24. Hide Caption 6 of 34 Photos: Unrest in Ferguson Police in riot gear move past a burning vehicle on November 24. Hide Caption 7 of 34 Photos: Unrest in Ferguson A looter in Ferguson walks out of a burning Walgreens on November 24. Hide Caption 8 of 34 Photos: Unrest in Ferguson Riot police clash with protesters on November 24. Hide Caption 9 of 34 Photos: Unrest in Ferguson Firefighters work on extinguishing a Little Caesars restaurant on November 24. Hide Caption 10 of 34 Photos: Unrest in Ferguson Smoke fills the streets of Ferguson as buildings burn on November 24. Hide Caption 11 of 34 Photos: Unrest in Ferguson Police officers grab a protester on November 24. Hide Caption 12 of 34 Photos: Unrest in Ferguson A woman treats her face for possible tear gas exposure on November 24. Hide Caption 13 of 34 Photos: Unrest in Ferguson People walk away from a burning storage facility on November 24. Hide Caption 14 of 34 Photos: Unrest in Ferguson A man steps out of a vandalized store on November 24. Hide Caption 15 of 34 Photos: Unrest in Ferguson A police officer runs by a burning police car on November 24. Hide Caption 16 of 34 Photos: Unrest in Ferguson Police officers stand guard as protesters confront them on November 24. Hide Caption 17 of 34 Photos: Unrest in Ferguson Protesters block streets in St. Louis after the announcement of the grand jury's decision on November 24. Ferguson is a suburb of St. Louis. Hide Caption 18 of 34 Photos: Unrest in Ferguson Police confront protesters in Ferguson on November 24. Hide Caption 19 of 34 Photos: Unrest in Ferguson A police officer points his rifle at demonstrators on November 24. Hide Caption 20 of 34 Photos: Unrest in Ferguson Protesters run for shelter as smoke fills the streets of Ferguson on November 24. Hide Caption 21 of 34 Photos: Unrest in Ferguson The glass windows of a store are shattered on November 24. Hide Caption 22 of 34 Photos: Unrest in Ferguson A demonstrator listens to a car radio as the grand jury's decision is delivered in front of the Ferguson Police Department. Hide Caption 23 of 34 Photos: Unrest in Ferguson Lesley McSpadden, mother of Michael Brown, is escorted away from the Ferguson Police Department on November 24. Hide Caption 24 of 34 Photos: Unrest in Ferguson A group of protesters vandalizes a police vehicle in Ferguson on November 24. Hide Caption 25 of 34 Photos: Unrest in Ferguson Police officers confront protesters on November 24. Hide Caption 26 of 34 Photos: Unrest in Ferguson Demonstrators block traffic during a protest in front of the Ferguson Police Department on November 24. Hide Caption 27 of 34 Photos: Unrest in Ferguson Demonstrators gather outside the police station on November 24. Hide Caption 28 of 34 Photos: Unrest in Ferguson Protesters gather as they wait for the announcement of the grand jury decision on November 24. Hide Caption 29 of 34 Photos: Unrest in Ferguson Members of the media line up in a parking lot across from the Buzz Westfall Justice Center on November 24. Hide Caption 30 of 34 Photos: Unrest in Ferguson Residents begin to gather at the Michael Brown memorial ahead of the grand jury announcement. Hide Caption 31 of 34 Photos: Unrest in Ferguson National Guard troops arrive ahead of the grand jury announcement. Hide Caption 32 of 34 Photos: Unrest in Ferguson Members of the Missouri National Guard are escorted out of the Buzz Westfall Justice Center. Hide Caption 33 of 34 Photos: Unrest in Ferguson Demonstrators are confronted by police as they block a street before the grand jury announcement. Hide Caption 34 of 34

The shooting sparked worldwide protests and the Monday announcement of no indictment triggered another round of demonstrations that continued through the week and into the weekend.

As police and protesters clashed, a contentious national debate on race and law enforcement reopened, with many people complaining that police unfairly target black males. Wilson is white and Brown was black.

Wilson says he's sorry but his conscience is clear

'He's 112 days too late'

People gathered again Saturday on the streets of Ferguson. One protester, Monica Chambers told CNN affiliate KMOV that Wilson should have been out of a job much earlier.

"He's 112 days too late," she said. "He should have been fired on Day One."

Wilson had been a member of the Ferguson Police Department for six years. He had been on paid administrative leave since the incident.

According to the Post-Dispatch, Wilson said he's not receiving a severance package. He'd been negotiating his resignation for weeks, according to people close to the talks. The letter does not say what Wilson plans to do next.

Wilson, 28, cited security fears in his letter of resignation, which reads:

"I, Darren Wilson, hereby resign my commission as a police officer with the City of Ferguson effective immediately. I have been told that my continued employment may put the residents and police officers of the City of Ferguson at risk, which is a circumstance that I cannot allow.

"For obvious reasons, I wanted to wait until the grand jury made their decision before I officially made my decision to resign. It was my hope to continue in police work, but the safety of other police officers and the community are of paramount importance to me. It is my hope that my resignation will allow the community to heal. I would like to thank all of my supporters and fellow officers throughout this process."

Wilson's lawyer, Bruntrager, told CNN that Wilson had been in hidin g since days after the shooting, when he received a phone call saying his home address was circulating on the internet. He was mowing the grass at the time.

Former officer moved from house to house

"He had to leave the grass literally halfway mowed and he had to go into hiding because there are death threats against him, there are bounties on his head," he said.

He stayed under the radar by moving from house to house, including briefly living with one of his lawyers, and spending time watching movies in dark theaters to avoid detection.

During this time, Wilson married a fellow Ferguson police officer. According to a St. Louis County marriage license, Wilson on October 24 married Barbara Lynn Spradling, with whom he shares a home in St. Louis.

On Tuesday, Wilson told ABC News that Brown was the aggressor in the minutes before the shooting.

In an account that generally mirrored his testimony before the grand jury, Wilson said Brown had attacked him while the officer sat in his car, then fled. Wilson said he chased after Brown until Brown turned back toward him, refusing Wilson's commands to stop.

Wilson denied some witnesses' claims that Brown had his hands up when he was fatally shot. "That would be incorrect," Wilson said.

As Brown approached, Wilson said, he warned Brown to stop. When he didn't stop, Wilson fired his handgun.

"I had to. If I don't, he will kill me if he gets to me," Wilson said.

Brown, who had been hit, continued to come toward Wilson, the officer said. Wilson fired again and began backing away.

"He gets to about 8 or 10 feet, and as he does that he kind of starts to lean forward, like he's going to tackle me. And I look down the barrel of my gun and I fired and what I saw was his head, and that's where (the bullet) went."

Governor calls for special session

In other action related to Ferguson, Missouri Gov. Jay Nixon called for a special state legislative session to address "critical funding" needs for the National Guard and state police after violent protests in Ferguson this week.

In a late-night call with state legislative leaders Friday night, Nixon highlighted the session's urgency to ensure Guard members are paid on December 15, his office said in a statement.

Hundreds more protesters turned out late Friday after a quiet Thanksgiving, clashing with officers and National Guard troops outside the Ferguson Police Department.

As protesters stepped into the street, authorities rushed across to take them into custody -- pulling some to the ground and shackling them with plastic zip-tie cuffs.

At least 16 people were arrested, including one facing a charge of assault on a law enforcement officer. One officer was injured, police said.

The protests have spread beyond Ferguson.

Nationwide demonstrations included service disruptions at an Oakland, California, transit station and a march in New York City.