Newly released evidence in the Trayvon Martin murder trial shows the alleged killer, George Zimmerman, telling police that the unarmed teenager followed him, ambushed him, and said, while pummeling Mr. Zimmerman, “You’re going to die tonight.”

Zimmerman faces second-degree murder charges for shooting Trayvon in Sanford, Fla., in late February. Prosecutors say he “profiled” the 17-year-old boy, followed him against the advice of a 911 dispatcher, “confronted” Trayvon, and illegally shot him in an ensuing struggle.

The case set off a febrile national debate about racial profiling and gun laws when authorities initially did not charge Zimmerman, as Trayvon’s parents, civil rights leaders, and activists sought “Justice for Trayvon.”

Also on Wednesday, the Sanford police chief who oversaw the case, Bill Lee, was fired after local officials determined he had lost the trust of the city. Mr. Lee had defended his department’s decision to let Zimmerman go free, citing the state’s Stand Your Ground law and saying police had few reasons to disbelieve his claims of self-defense.

Florida Gov. Rick Scott (R) subsequently appointed a special prosecutor to reexamine the case, and 44 days after Trayvon’s death, that prosecutor, Angela Corey, filed a second-degree murder charge against Zimmerman.

The foundation of the prosecution’s case is that Zimmerman willfully broke the law by instigating and prosecuting an action against a minor who was unarmed and doing nothing wrong.

But the story that Zimmerman told the police the night of the shooting and the next day, captured on audio and videotapes and made public Wednesday, is much different. It presents a scenario that could be germane to the defense strategy: that, in Florida, a defendant can invoke Stand Your Ground, or no duty to retreat, as a defense even if an interaction occurred between the defendant and the victim before the shooting, so long as the defendant didn’t initiate the attack.

"Although Zimmerman was possibly negligent, irresponsible, and exercised poor judgment, it was not illegal for him to follow Martin, carry a gun when doing so or even ignore the opinion of the civilian 911 dispatcher when advised,” writes Mark NeJame, a well-known defense attorney from Florida, in an op-ed for CNN.

In the tapes, Zimmerman can be seen and heard telling police he called 911 to “report a suspicious person” loitering near the back door of a condo that had previously been broken into.

Zimmerman told police that, while he had the dispatcher on the phone, Trayvon circled his SUV. After that, Zimmerman told police he lost sight of Trayvon and got out of his car to find a street address for police to respond to. At that point, he said, the dispatcher asked whether he was following Trayvon and noted, “We don’t need you to do that.”

On his way back to the parked SUV, Zimmerman says on the tapes, Trayvon ambushed him and asked, “What the [expletive] is your problem?” “I don’t have a problem,” Zimmerman claims he said. The teenager responded by saying, “Now you have a problem,” Zimmerman recounted to police.

According to Zimmerman, Trayvon punched him in the nose, knocking him over, and then started “waling” on his head. Eventually, he said, the teenager appeared to reach for Zimmerman’s gun, at which point Zimmerman grabbed it himself and fired.

The tapes also include Zimmerman’s interaction with an investigator, Chris Serino, who pushed back at Zimmerman’s account, including whether the extent of his injuries – a broken nose and two scratches on the back of his head – were consistent with someone fearing for his life.

“The court of public opinion is going to beat up on you a lot," Mr. Serino told Zimmerman. "A lot of people don't think that your injuries are consistent with getting into a life-threatening type thing."

Serino then told Zimmerman that Trayvon had no criminal record and was a “Good kid. Mild-mannered kid … not a goon." After recounting another witness account that suggested Zimmerman was in the act of detaining Trayvon instead of being attacked by him, Serino asked Zimmerman bluntly, “You got any problems with black people?” “No, sir,” Zimmerman said.

Serino also questioned Zimmerman about why he needed to get out of the car to figure out the street names in a subdivision he’d lived in for three years. Zimmerman patrolled the area regularly as the volunteer captain of a neighborhood watch program and had made dozens of 911 calls about problems in the area.

"To be honest with you, I have a bad memory anyway," Zimmerman said.

The evidence, released by Zimmerman’s defense team as part of the discovery phase of the trial, includes audio and video tapes taken of Zimmerman in the hours after Trayvon’s death, as well as during the following few days, when Zimmerman, at one point, reenacted parts of what he said took place.

The tapes become public at a time when Zimmerman’s credibility has taken a hit. Florida Circuit Judge Kenneth Lester decided on June 1 to withdraw the defendant's bond after prosecutors shared phone recordings revealing that Shellie Zimmerman, Zimmerman's wife, had lied to the court when she said the family did not have any money although they had more than $135,000 in their accounts, and that the couple had colluded to hide the money from authorities.

Zimmerman will appear at a new bond hearing next week to try to explain to the judge what happened, and ask for leniency.