The jury in the George Zimmerman trial was given the option Thursday of convicting the former neighborhood watch captain on the lesser charge of manslaughter in the shooting death of 17-year-old Trayvon Martin.

Because of the judge's ruling, the six jurors now have three options when they start deliberations as early as Friday: Guilty of second-degree murder, guilty of manslaughter and not guilty. 

To win a second-degree murder conviction, prosecutors must prove Zimmerman showed ill will, hatred or spite — a burden the defence has argued the state failed to meet. To get a manslaughter conviction, prosecutors must show only that Zimmerman killed without lawful justification.

Zimmerman profiled 17-year-old Trayvon Martin assuming he was up to no good, and that led to the Miami teen's death, a prosecutor said Thursday in closing arguments.

"A teenager is dead. He is dead through no fault of his own," prosecutor Bernie de la Rionda told jurors. "He is dead because a man made assumptions … Unfortunately because his assumptions were wrong, Trayvon Benjamin Martin no longer walks this earth."

De la Rionda told the jury that Zimmerman wanted to be a police officer and that's why he followed Martin through his neighbourhood even though the teen wasn't doing anything wrong.

"He assumed Trayvon Martin was a criminal. That is why we are here," de la Rionda said.

Prosecutors began their closing arguments after the judge presiding over the trial ruled that jurors can consider the lesser charge of manslaughter, but she denied a request for the jury also to consider third-degree murder after a defence attorney called the proposal "outrageous."

Prosecutor Richard Mantei argued that instructions for third-degree murder should be included on the premise that Zimmerman committed child abuse when he fatally shot 17-year-old Trayvon Martin because Martin was underage.

But defence attorney Don West called the proposed instruction "a trick," and he accused the prosecutor of springing it on the defence at the last minute.

"Just when I didn't think this case could get any more bizarre, the state is alleging child abuse?" West said. "This is outrageous. It's outrageous the state would seek to do this at this time."

Question of proving intent

Judge Debra Nelson denied the third-degree murder instruction, saying she was exercising caution since she was unsure if prosecutors could prove intent.

"I just don't think the evidence supports that," Nelson said.

The judge, however, agreed with the prosecution that jurors could consider manslaughter as a lesser charge.

West said he wanted the six jurors to only consider the second-degree murder charge or not guilty.

"The state has charged him with second degree murder. They should be required to prove it," West said.

Zimmerman has pleaded not guilty to second-degree murder. On the night of the fatal scuffle in February 2012, Martin was visiting his father and his father's fiancee at the same townhome complex where Zimmerman lived.

Zimmerman observed Martin while driving in his neighbourhood, called police and the fight ensued after the neighbourhood watch volunteer got out of his vehicle. Zimmerman claims Martin was slamming his head into the concrete pavement when he fired his gun.

Some civil rights activists argued that a delay in charging Zimmerman was influenced by Martin's race, and protests were held around the nation in the 44 days between the fatal fight and Zimmerman's arrest. Martin was black and Zimmerman identifies himself as Hispanic.