The Supreme Judicial Court on Tuesday gave Suffolk County prosecutors a choice: They can retry Mario Gonzalez for stabbing his girlfriend to death in 2009 or they can accept reducing his current conviction from first to second-degree murder.

A first-degree murder conviction carries a mandatory sentence of life without parole. A second-degree conviction also carries a life sentence but with the possibility of parole, as early as 15 years after conviction.

At issue is the legal theory under which prosecutors charged Gonzalez with first-degree murder and the judge's instructions to his jury.

Prosecutors did not allege that Gonzalez planned Luz Forty's murder in his Ridgewood Street apartment on Feb. 15, 2009. Instead, they said he deserved to be sent away for life because of the "extreme atrocity or cruelty" in the way he killed her during an argument over his drinking - he stabbed her eight times in the chest and shoulders.

The problem, the state's highest court ruled, was that:

"The judge did not instruct the jury that they could consider any credible evidence of the defendant's consumption of alcohol in determining whether the defendant committed the killing with extreme atrocity or cruelty, an instruction that in substance is required where there is evidence that the defendant was under the influence of alcohol at the time of the killing. ...

"Where the jury did not find the defendant guilty on the theory of deliberate premeditation, where the defendant was the first to telephone 911 after the stabbing, and where there was no evidence of a history of domestic abuse, we cannot say that 'we are substantially confident that, if the error had not been made, the jury verdict would have been the same.'