Reginald Tanubagijo, 54, was taken into custody at NorthBay Medical Center, where he was being treated for self-inflicted wounds, Suisun City police said.
Tanubagijo had been arrested on suspicion of felony child abuse for allegedly assaulting the infant on Nov. 29 at a home at 1613 Youngstown Lane in Suisun City, police said.
The child was taken to the NorthBay Medical Center then to Children's Hospital in Oakland and listed in grave condition.
Tanubagijo was arrested in connection with the incident the next day but posted bail and was released from jail.
At 9:20 a.m. Sunday, police received a frantic call requesting medical assistance at Tanubagijo's home and found Tanubagijo unresponsive and wounded, police said. He was taken to NorthBay Medical Center.
Several hours later, shortly after 2 p.m. Sunday, police learned the infant had succumbed to his injuries and they arrested Tanubagijo on suspicion of murder.
Tanubagijo was still at the hospital for treatment of his wounds and a psychological evaluation this morning, Cmdr. Tim Mattos said.