Destin Marcelin, 6, died in a Dorchester apartment last month when his father, Patrick Marcelin, smothered or strangled him - or maybe both, Boston Police and the Suffolk County District Attorney's office report.

Marcelin then slashed his wrists, then plunged a knife into his chest after opening the door of a Mattapan apartment to police after they had tracked him down two days later.

In a statement, police and the DA's office say:

"The Office of the Chief Medical Examiner has declared the child's Sept. 4 death to be the result of “homicidal asphyxia” by smothering, pressure on his neck or chest, or some combination of the two. After a thorough review of the evidence gathered since that time, police and prosecutors believe his father, Patrick Marcelin, 49, of Mattapan was responsible. ...

"Because the sole suspect is deceased, and because no evidence suggests wrongdoing by any other person in connection with Destin Marcelin's death, [DA Dan] Conley and [Police Commissioner William] Evans stated that criminal charges would not be sought in the case. ...

"Destin was found unresponsive in bed on the morning of what would have been his first day of school. He had spent the night with his father at the Devon Street home of relatives. Patrick Marcelin left the home at about 7:20 a.m., telling others in the household that Destin was sleeping. Another adult later found Destin in bed, felt him to be cold to the touch, and called 911. Boston EMS responded just after 9:30 a.m. with Boston Police and declared him dead at the scene."