A five-month-old boy is fighting for his life at Toronto's Hospital for Sick Children while police search for the man they suspect of beating him.

"It's a tragic thing, but we all try to stick together," the boy's aunt told CTV Toronto on Friday.

"You think to yourself, 'Why him? What did he do to deserve this?'"

The woman said her infant nephew has undergone three hours of brain surgery and is on life support. "We just pray," she said.

Police are looking for Ronnie Munoz-Hernandez, 21.

He had recently moved in with the boy's mother, living with her and the baby in a west-end highrise apartment. He was alone with the boy on Saturday when the injuries allegedly occurred, but the boy wasn't taken to hospital right away.

The aunt said the mother found her son unresponsive on Sunday.

Munoz-Hernandez came with the mother to hospital on Sunday. But after the boy was taken in by emergency doctors, he quietly walked out of the hospital, CTV Toronto reported.

"When the nurses told her (her son had) been beaten, she couldn't believe it," the aunt said. "When she went to look for (Munoz-Hernandez), he was gone."

Police released Munoz-Hernandez's photo on Thursday. They are seeking him on a charge of aggravated assault.

Extra officers from 12 Division have been assigned to the case. Munoz-Hernandez's photo has been supplied to the bus depot, train stations and airports in case he attempts to leave town.

People with information are asked to call 12 Division at 416-808-1200, Crime Stoppers anonymous at 416-222-TIPS (8477) or online at www.222tips.com. They can also text to TOR plus message to CRIMES (274637).

No allegations against Munoz-Hernandez have been proven in a court of law.

With a report from CTV Toronto's Sneha Kulkarni