SANFORD, Fla. » Before the night of Trayvon Martin’s fatal shooting, neighborhood watch volunteer George Zimmerman called police close to 50 times over the previous eight years to report such things as slow vehicles, loitering strangers in the neighborhood and open garages.

Now prosecutors want to introduce recordings of those past calls in Zimmerman’s trial and planned to try to convince Judge Debra Nelson today that the calls he made in the months before the shooting are indicative of his state of mind on the night the unarmed teen was killed.

State attorney John Guy said in his opening statement Monday that Zimmerman thought Martin was one of the "F——— punks" who "always get away" whom he’d observed previously in his neighborhood and called police about.

But late Monday, defense attorneys objected to the introduction of the previous calls during the questioning of a witness. The defense maintains they should not be admissible under the rules of evidence.

The judge said she would address the matter today and sent the jurors to the hotel where they are being sequestered for the duration of the trial, which could last several weeks.

When Zimmerman initially wasn’t charged in the fatal central Florida shooting, Martin’s family claimed Zimmerman had racially profiled Martin and police were dragging their feet in bringing charges. Zimmerman, whose mother is Hispanic and whose father is white, has denied the confrontation had anything to do with race.

The prosecution began opening statements in the long-awaited murder trial with shocking language, repeating obscenities Zimmerman uttered while talking to a police dispatcher moments before the deadly confrontation.

The defense opened with a knock-knock joke about the difficulty of picking a jury for a case that stirred nationwide debate over racial profiling, vigilantism and Florida’s expansive laws on the use of deadly force.

"Knock. Knock," said defense attorney Don West.

"Who is there?"

"George Zimmerman."

"George Zimmerman who?"

"All right, good. You’re on the jury."

Zimmerman, 29, could get life in prison if convicted of second-degree murder for gunning down Martin on Feb. 26, 2012, as the black teenager, wearing a hoodie on a dark, rainy night, walked from a convenience store through the gated townhouse community where he was staying.

Randy McClean, a criminal defense attorney in Florida with no connection to the case, called the prosecution’s opening statement "brilliant" in that it described Zimmerman’s state of mind. But he described the knock-knock joke as less than stellar.

"If you’re defending your client for second-degree murder, you probably shouldn’t start your opening with a joke," McClean said.

Guy’s first words to the jury recounted the profane words Zimmerman told a dispatcher in a call shortly after spotting Martin: "F——— punks. These a———-. They always get away."

Zimmerman was profiling Martin as he followed him, Guy said. He said Zimmerman viewed the teen "as someone about to a commit a crime in his neighborhood."

"And he acted on it. That’s why we’re here," the prosecutor said.

Zimmerman didn’t have to shoot Martin, Guy said. "He shot him for the worst of all reasons: because he wanted to," he said.

The prosecutor portrayed the then-neighborhood watch captain as a vigilante, saying, "Zimmerman thought it was his right to rid his neighborhood of anyone who did not belong."

West told jurors a different story: Martin sucker-punched Zimmerman and then pounded his head against the concrete sidewalk, and that’s when Zimmerman opened fire.

Showing the jury photos of a bloodied and bruised Zimmerman, the defense attorney said, "He had just taken tremendous blows to his face, tremendous blows to his head."

West said the idea that Martin was unarmed is untrue: "Trayvon Martin armed himself with a concrete sidewalk and used it to smash George Zimmerman’s head."

The prosecutor, however, disputed elements of Zimmerman’s story, including his claim that Martin put his hands over Zimmerman’s mouth and reached for the man’s gun. Guy said none of Zimmerman’s DNA was found on Martin’s body, and none of the teenager’s DNA was on the weapon or the holster.

But West said that doesn’t prove anything, arguing that crime-scene technicians didn’t properly protect Martin’s hands from contamination.

Two police dispatch phone calls that could prove to be important evidence for both sides were played for the jury by the defense. Martin’s mother, Sybrina Fulton, left the courtroom before the second recording, which has the sound of the gunshot that killed Martin.

The first was a call Zimmerman made to a nonemergency police dispatcher, who told him he didn’t need to be following Martin.

The second 911 call, from a witness, captures screams in the distant background from the struggle between Zimmerman and Martin. Martin’s parents said the screams are from their son, while Zimmerman’s father contends they are his son’s.

Nelson ruled last weekend that audio experts for the prosecution won’t be able to testify that the screams belong to Martin, saying the methods used were unreliable.

Other witnesses who testified Monday included a convenience store clerk and the 911 dispatcher who took Zimmerman’s call when he was following Martin, who had gone to the convenience store to buy Skittles and a can of iced tea.

The 911 dispatcher, Sean Noffke, testified that he had advised Zimmerman not to follow Martin.

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Follow Kyle Hightower on Twitter at http://twitter.com/KHightower

Follow Mike Schneider on Twitter at http://twitter.com/MikeSchneiderAP