Aggravated manslaughter charges were filed Saturday against 19-year-old Daquan Davis.
Prosecutors say Davis shook his girlfriend's infant son to death.
Davis also faces child endangerment charges in the death of the 6-month-old child.
Acting County Prosecutor Jim McClain says Davis was caring for the infant while the child's mother was at work. When she returned home around 4 a.m. Friday, she found the boy was unresponsive and called 911.
The child was pronounced dead a short time later, and authorities were notified.
A joint investigation by the prosecutor's office and Atlantic City authorities ensued, and Davis was arrested late Friday night.
He is being held on $750,000 bail.
The Associated Press contributed to this report.