His murder trial is already two weeks old, but the case against a Florida neighbourhood watch leader George Zimmerman over the death of the unarmed black teenager Trayvon Martin gets under way in earnest on Monday when prosecutors and defence lawyers deliver their long-awaited opening statements.

Nine days of jury selection, interspersed with aggressive legal debate over the admissibility of certain expert testimony, has provided a glimpse of the passionate arguments expected inside a Sanford courtroom over the next two to four weeks.

The state's prosecution team, led by assistant state attorney Bernie de la Rionda, will attempt to portray Zimmerman, 29, as an overzealous, self-appointed custodian of his gated community who pursued, confronted, then shot a black youth in a hoodie whom he assumed was up to no good.

Their case was buoyed by a number of pre-trial rulings by judge Debra Nelson that excluded evidence about 17-year-old Martin's drugs use and suspension from school but allow de la Rionda to use phrases such as "wannabe cop" and "vigilante" to describe Zimmerman in his opening statement.

Lawyers for Zimmerman, who denies second-degree murder on the grounds of self-defence, will claim Martin initiated their confrontation as he walked through the Retreat at Twin Lakes development on 26 February last year. They will say Martin broke the defendant's nose with a punch and smashed his head on a concrete pavement, leaving their client no option but to fire the single shot that killed the teenager.

An all-female jury of six will begin hearing testimony on Monday after listening to both sides' opening arguments, with Zimmerman facing at least 25 years in jail if he is convicted.

"This is not a legally complex case and there are few pieces of evidence that are truly relevant," Jasmine Rand, one of the attorneys representing the Martin family, said.

"We know George Zimmerman pulled the trigger, we know Trayvon Martin had no blood on his hands. The irrelevant evidence mischaracterising Trayvon has been shot down. We have every confidence in the prosecution to bring justice."

Lengthy disputes over what evidence could be introduced lasted right up to the weekend, with Nelson issuing her final pre-trial ruling only on Saturday.

In what some analysts see as a significant victory for Zimmerman, and his lead attorney Mark O'Mara, evidence from two voice analysis experts over a 911 call made by a resident on the night of the shooting cannot form part of the prosecution's case.

One of the expert witnesses testified that he was able to rule out Zimmerman as the man heard screaming on the recording, which also captured the fatal gunshot. The second said he was certain it was Martin's voice yelling "I'm begging you" and "Stop".

O'Mara, however, argued successfully that the science behind their testimony failed to meet Florida's stringent legal standards and Judge Nelson ordered that neither expert could take the stand during the trial because it would "confuse issues [and] mislead the jury".

But she did leave the door open for the prosecution by saying her ruling "does not prevent the parties from playing the tapes at trial or from calling witnesses familiar with the voices of the defendant or Martin to testify to the identity of the person(s) making the screams".

That raised the prospect of a powerful appearance on the stand of Martin's mother, Sybrina Fulton, who has insisted that she recognised her son's voice on the recording.

One key prosecution witness is expected to be a girlfriend of Martin's, who claims she was on the phone to him immediately before he was shot, and said that he told her he was being pursued as he made his way to the house of a friend of his father. The defence has already announced its intention to attack her credibility.

Martin's death sparked weeks of protests by thousands in central Florida and elsewhere because Zimmerman was freed without charge on the night of the shooting. He was arrested and charged six weeks later, only after state governor Rick Scott appointed a special prosecutor to re-examine the case, a development that ultimately cost the chief of the Sanford police department his job.

Civil rights leaders attempted to portray the case as a racial issue, with an unarmed black teenager gunned down by an attacker of mixed white-Hispanic descent who would otherwise have escaped a trial.

"This is not an easy process, in fact it's been very painful for Trayvon's family, but they take comfort from knowing that George Zimmerman is facing a jury of his peers and is being brought to justice," Ms Rand said.

"If George Zimmerman is convicted, it would send a message to the nation that you can't behave as a vigilante and expect it to be unpunished, that people are no longer going to be silent about an attempt at a miscarriage of justice.

"When that bullet pierced Trayvon Martin's heart, it awakened America from a stupor of complacency."