A 4-month-old boy, found dead in November, was the victim of a homicide, and the four family members who were in the home no longer are cooperating with law-enforcement officials, Upper Darby Police Superintendent Michael Chitwood said Sunday.

The child, Ja'Den Jones, died of "blunt craniocervical trauma," according to autopsy results, which Chitwood released.

The family members "have all hired lawyers and our investigation is kind of stymied," he said. "This shows to me that there is a conspiracy to obstruct police from finding out what happened to the child. That baby was killed in that house. That baby was hurt by one of the four people in that house, and the bottom line is there is no voice for the baby."

On Nov. 6, police were called to the infant's home in the 100 block of N. Fairview Avenue at 3:30 a.m. after relatives reported finding him unresponsive in his crib. He was not breathing and had no pulse, and was transported to Delaware County Memorial Hospital. He was transferred to Children's Hospital of Philadelphia, where he died Nov. 10.

The child's mother; 38, sister, 17; cousin, 21, and a male family friend, 38, were in the house when the child was found, Chitwood said. He declined to give any of their names.

The baby showed no signs of trauma, and family members initially cooperated with police, Chitwood said. The mother had left the house to attend a fund-raising event and returned home at 3:30 a.m to find the child unresponsive in his crib.

Contact Miriam Hill at 215-854-5520 or hillmb@phillynews.com or on Twitter @miriamhill. Read the City Hall politics blog at www.heardinthehall.com.