Three-month-old Angel Mendoza had a skull fracture and a lacerated liver. Both caused internal bleeding.
Doctors knew the injuries weren't caused by a fall in the bathtub, as the infant's father claimed.
According to the Las Vegas police arrest report for the baby's father, Andrew Mendoza, the infant had adult-sized bite marks and bruises all over his body. He had widespread retinal hemorrhaging, consistent with having been shaken.
The baby's injuries were so severe that he was nonresponsive when police arrived at Mendoza's apartment Monday.
When the baby boy was taken to University Medical Center, he was breathing, but not on his own. Angel remains in critical condition.
When police first interviewed Mendoza, the 21-year-old said that his son had fallen in the bathtub, according to the report. He later changed his story.
The report said he admitted to detectives that he bit Angel's right cheek, right arm, chest area, and right leg after the infant woke him Saturday morning.
"Andrew also stated that he would also pinch Angel in various parts of his body when he would cry," the report states.
Angel's mother, who has been in Arizona since early February, "advised him to stop doing that."
Mendoza would get frustrated when Angel cried or didn't eat. He once squeezed the baby against his chest so tightly that Angel vomited on him, according to the report.
The bruises to Angel's forehead came from Mendoza throwing a baby bottle at him when he wouldn't eat.
On Sunday, Mendoza took a fist, placed it on Angel's abdomen, and put all his weight onto it, the report states.
Mendoza, who remained at the Clark County Detention Center on Thursday on $48,000 bail, was arrested on one count of child abuse with substantial bodily harm, eight counts of child abuse, one count of child endangerment and one count of child neglect.