(CNN) -- George Zimmerman, the neighborhood watch volunteer charged with murder in the February death of Trayvon Martin, has been released on bail from a Florida jail.
Zimmerman walked out of the John E. Polk Correctional Facility in Sanford, Florida, around midnight Sunday, wearing a brown jacket and blue jeans and carrying a brown paper bag in his arms. He got into the back of a white BMW and did not speak to reporters.
It was not immediately known where he was headed. Family members and Zimmerman's attorney, Mark O'Mara, have stressed the need for secrecy regarding Zimmerman's destination. Both he and his family have received threats, they said.
Seminole County Sheriff's Office said Zimmerman had been fitted with a GPS monitoring device allowing authorities to track his location.
The release came as something of a surprise. Over the weekend, his lawyer had said Zimmerman might remain behind bars until the middle of this week as his team worked to secure funds to meet the $150,000 bond set Friday.
With the 10% cash payment customarily made to secure bond, Zimmerman's family needed $15,000 for him to make bail.
Prosecutors had asked that Zimmerman's bond be set at no less than $1 million, citing a 2005 scrape with a police officer and a domestic violence injunction against Zimmerman.
Martin's family wasn't pleased by news of Zimmerman's release, said one of their attorneys, Daryl Parks.
"It's tough for them to see their son's killer walk free again," he said.
Zimmerman is accused of shooting Martin, 17, after calling authorities to report a suspicious person walking around his Sanford, Florida, neighborhood.
Zimmerman claims the unarmed teen attacked him. Martin's supporters say Zimmerman targeted Martin because he was black.
The case has has riveted the nation and sparked intense discussions about race and gun control.
For his part, Zimmerman, 28, remains "very worried" about his situation, O'Mara said Saturday, before his client's release.
During his bond hearing Friday, Zimmerman apologized to Martin's family.
"I wanted to say I am sorry for the loss of your son," he said in an unusual appeal directly to Martin's family before he testified in the Seminole County Courthouse in Sanford. "I thought he was a little bit younger than I was, and I did not know if he was armed or not."
O'Mara said after the hearing that his client was responding to an interview in which Martin's mother, Sybrina Fulton, said she wanted to hear from the man who shot her son.
"He didn't want to defend himself, he didn't want to discuss the facts of the case. He heard the request of the family, and he wanted to respond to it," O'Mara said, adding that an attempt to apologize to the family in private was rebuffed.
Lawyers for Martin's family, however, called the apology a self-serving act by a man facing a life sentence in prison if convicted.
"This was the most disingenuous, insulting thing I've ever seen," said Martin family attorney Natalie Jackson.
Assistant State Attorney Bernie de la Rionda had argued for a higher bond total. Prior run-ins with a police officer and a woman who named him in a domestic violence injunction show that Zimmerman is violent and a threat to the community, de la Rionda said.
Lester, however, described the incidents as "run of the mill" and "somewhat mild" in approving O'Mara's request for bond.
Although details of the shooting remain murky, what is known is that Martin ventured out on February 26 from the home of his father's fiancée in Sanford and went to a nearby convenience store, where he bought a bag of Skittles and an Arizona Iced Tea.
On his way back, he had a confrontation with Zimmerman, who shot him.
Zimmerman had called 911 to complain about a suspicious person in the neighborhood.
In the call, Zimmerman said he was following Martin after the teen started to run, prompting the dispatcher to tell him, "We don't need you to do that."
Zimmerman told authorities that he first briefly lost track of Martin, then the teenager approached him and the two exchanged words. Zimmerman said he reached for his cell phone, then Martin punched him in the nose. Zimmerman said Martin pinned him down and began slamming his head onto the sidewalk, leading to the shooting.
A police report indicated Zimmerman was bleeding from the nose and the back of his head.
Zimmerman's father testified Friday that when he saw his son the day after Martin's shooting, he was wearing a protective cover over his nose, his face was swollen, and he had two vertical gashes on his head. He also reportedly suffered a broken nose.
Martin's family and the special prosecutor appointed to investigate the case have rejected Zimmerman's self-defense claim, saying they believe Zimmerman disobeyed the instructions of a police dispatcher to stop following Martin, racially profiled him and unjustly killed him.
Police have said Zimmerman was not immediately charged because there was no evidence to disprove his account that he had acted in self-defense.
O'Mara said Saturday that he expects the prosecution was holding back some evidence that is key to its case during Friday's court hearing.
"I'm sure the state has a lot more information," the lawyer said, describing what was presented Friday as "snippets of the evidence." "I'm just looking forward to getting it."
CNN's Vivian Kuo, Leslie Tripp Holland and Holly Yan contributed to this report.