Police are looking for Francisco Sao, 23, on suspicion of homicide by abuse and/or second-degree murder, KIRO 7 Eyewitness News reporter Kevin McCarty said.

Sao was still at large as of Saturday.

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The Pierce County Medical Examiner's Office said Trumane Sao died of blunt-force trauma to the abdomen, and it said the case is a homicide.

Detectives said Francisco Sao had been alone with the child after he and the infant's mother got into a fight.

Francisco Sao, wanted in baby beating Francisco Sao Francisco Sao

The baby's mother left the couple's Lakewood apartment and returned to find the child having trouble breathing on Wednesday, police told KIRO 7 Eyewitness News reporter Kevin McCarty.

The boy's stomach was bruised, and the father told the mother "he hit the baby in the stomach," according to police.

Lakewood police and paramedics were called to the apartment. A neighbor performed CPR on the child until medics arrived and took him to St. Clare Hospital, where he was pronounced dead at 11:25 p.m.