PORTLAND, Maine — The Maine Supreme Judicial Court on Tuesday unanimously upheld the conviction of a Bangor man found guilty of manslaughter in the Nov. 25, 2012, death of his 3-month-old son, Xander Brown.

Dustin Brown, 23, was sentenced to 12 years in prison with all but 4½ years suspended to be followed by four years of probation following a jury-waived trial.

Justices heard oral arguments in the appeal in February at the Cumberland County Courthouse.

Experts for the prosecution during the trial said the baby died of bleeding and tearing in his brain, an injury most likely caused by violent shaking. A defense expert said he died of cardiac arrest after choking on formula.

Brown, who did not take the stand, told police he was alone and feeding his son when the baby suddenly went limp. The infant’s mother, Alaina Cain Stacy, now 20, of Bangor, testified that Brown told her he had been feeding Xander, and when he went to burp him Xander’s head struck his chin.

Jamesa Drake, the Auburn attorney who represented Brown in the appeal, argued that her client should have a new trial because the prosecution had not proved exactly what the defendant did to cause the baby’s death.

The justices disagreed.

“A rational fact finder [the judge] could reasonably infer from the record that, when he was alone with [Xander], Brown handled the infant with such force that the infant sustained subdural, subarachnoid, optic nerve sheath and retinal hemorrhages, and that Brown’s failure to be aware of the risk that his handling of the infant in that manner could produce death was ‘a gross deviation from the standard of conduct that a reasonable and prudent person would observe in the same situation,’” Justice Ellen Gorman wrote for the court.

Brown has been free on bail pending the law court’s decision. Once his attorney receives official notice of the decision, Brown will have seven days to return to prison.

He is expected to be credited for the more than seven months he served prior to his release in October.