MIAMI (Reuters) - "You're going to die tonight" were among the last words Florida neighborhood watch volunteer George Zimmerman heard from Trayvon Martin before he shot and killed the unarmed black teenager, Zimmerman told police.

The death threat came as Martin was pounding his head into the ground and trying to smother him, according to Zimmerman's statements to detectives in the central Florida town of Sanford soon after the killing on a rainy night in February.

Audio recordings of the statements were released by Zimmerman's lawyers late Wednesday, giving the public the opportunity to hear Zimmerman's account of what happened on the night of February 26 in his own words for the first time.

The outline of Zimmerman's account has been known for months. The deadly encounter began when Zimmerman spotted Martin walking slowly through a gated community in Sanford, and reported him in a non-emergency call to police as a suspicious person.

He began following Martin but then lost track of him, only to have him reappear suddenly and punch him to the ground.

According to Zimmerman, Martin then got on top of him and began beating him, repeatedly slamming his head into the concrete sidewalk.

"He just started punching me in the face and I started screaming for help," Zimmerman told detectives in one of the tapes released by his lead attorney Mark O'Mara.

"I couldn't see and I couldn't breathe ... He grabbed my head and started hitting it into the sidewalk," he said.

"I could see people looking and some guy yells out 'I'm calling 911' and I says 'help me, help me, he's killing me,'" Zimmerman said.

"And he (Martin) puts his hand on my nose and on my mouth, and he says 'you're going to die tonight' and I don't remember much after that ... I couldn't breathe and he still kept trying to hit my head."

POLICE CHIEF FIRED

Zimmerman then recalls, however, that he felt Martin's hand go down his side and he thought he was reaching for the handgun he was carrying in a holster attached to his waistband.

"I thought he was going for my firearm so I grabbed it immediately and as he banged my head again I just pulled out my firearm and shot him."

In a written statement to police, also made public by O'Mara, Zimmerman recalls what then happened as his fatal encounter with Martin ended with a lone gunshot to the young man's chest.

"The suspect sat back allowing me to sit up and said "you got me," Zimmerman wrote in the sworn statement.

"At this point I got in top of the suspect, holding his hands away from his body."

The release of Zimmerman's statements to police came soon after Sanford officials announced that the police chief whose department initially failed to arrest Zimmerman was fired on Wednesday.

Sanford Police Chief Bill Lee had been on paid leave since March 22 amid outrage over his handling of the racially charged case.

Lee contended that Zimmerman was protected under Florida's "Stand Your Ground" law, which gives people who feel threatened broad latitude to use deadly force to defend themselves.

Zimmerman, who is back in custody after the recent overturning of his release on bond, has since been charged with second-degree murder and faces 25 years to life imprisonment if convicted at a trial for which no date has yet been set.