A 9-month-old baby who died in the Bronx in February was killed by the synthetic opioid fentanyl, officials said Thursday.

Police responding to a 911 call on Feb. 14 found little Dante Steer-Cooman unconscious and unresponsive in a home in the Wakefield section. The infant was taken to Montefiore Hospital, where he was pronounced dead.

Police said there were no obvious signs of trauma on the boy’s body. But the city medical examiner’s office classified the death as a homicide on Wednesday. A spokesperson for the office said Thursday that the cause of death was acute fentanyl intoxication.

Police have made no arrests. The investigation is ongoing.