A 23-year-old Rochester man who caused life-threatening injuries to a 4-month-old last year was sentenced to four years in prison on Monday.

James John Mentz was convicted in Mower County Court of felony malicious punishment of a child; felony first-degree assault with great bodily harm was dismissed. Mentz was given credit for 161 days already served in jail.

According to police reports, Mentz and his girlfriend, who is the victim’s mother, took the 4-month-old to Mayo Clinic Health System in Austin at about 7 p.m. July 28, 2011, as the infant suffered a head injury. Police were dispatched after hospital officials grew concerned over the injury, as Mentz claimed the baby fell out of a chair. The baby was airlifted to St. Marys Hospital that night.

Mentz later told police he put the infant in a large chair with pillows in the living room about two feet off the ground and stepped into the kitchen to get a baby bottle. Mentz said he heard a thud and a rattle and discovered the baby on the ground crying, according to the police report. He said he contacted his girlfriend about the injuries but wanted to wait for her to make the decision about going to the hospital.

The girlfriend’s brother offered to take Mentz and the infant to the hospital, but Mentz refused and said he’d rather wait for his girlfriend. The brother told police the infant’s eyes were closed, and he wasn’t really moving.

When the girlfriend got home, she saw swelling on the back of the infant’s head. She told police she asked why Mentz hadn’t taken the infant to the hospital.

Hospital officials told police the large bumps on the back of the baby’s head weren’t consistent with a 2-foot fall, even if the baby had hit his head on a nearby swing chair, according to police. The baby was diagnosed with several skull fractures, acute and chronic subdural hematomas, and retinal bleeding, among other conditions. There was evidence of new and old bleeding into the baby’s brain as well, according to the police report. At the time of the report, the infant had increased instances of seizures and was sedated on a ventilator for a time.

The Mower County Attorney’s office could not release an update on the child’s condition.

The girlfriend told police the baby had been ill for a month before the injuries, acting spaced out at times before coming back to his normal self. The infant also got sick and projectile vomited for several days, which caused Mentz and the mother to have the infant hospitalized for two days.

Mentz violated his conditional release in April after testing positive for cocaine use. He was also convicted of third-degree burglary in 2009.

—Trey Mewes contributed to this report.