Authorities have said they were called to Sullivan's Radcliffe Street home in Bristol last May 25 to find his 4-month-old son Timothy was "not breathing and cold to the touch."
Officers performed life-saving measures but eventually took the baby to Lower Bucks Hospital where he died.
Medical staff at the hospital said the boy's injuries were "indicative of a battered child" — he suffered "contusions, bruising, and abrasions" throughout his body, the DA's Office said at the time.
The Coroner's Office ruled he died from multiple blunt force injuries by manner of homicide.
Investigators determined Sullivan "violently shook" his son at least two times last May 24 and "at least six additional times" in as many weeks before that.
Sullivan, 30, has a sentencing hearing scheduled for Aug. 29, according to court records.
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