An autopsy has found that a 3-month-old baby boy was murdered before being thrown onto a Galveston roadside, still strapped into his car seat.

The infant's death was ruled a homicide by blunt force head trauma, said John Florence, chief investigator for the Galveston County Medical Examiner's Office.

Police in Texas have identified the biological father of the baby, the last person known to be with the child, and are calling him a person of interest in the infant’s death, according to MyFoxHouston.

A search was under way for Travis Mullis, 21, after an Alvin woman, whose name hasn't been released, tentatively identified the body as that of her son. She contacted police on Tuesday, saying she hadn't seen her son since Mullis took him that morning.

A couple who were bird-watching discovered the baby’s body Tuesday afternoon after first mistaking it for a doll.

The couple believed to be the baby's parents had argued the night before the infant was killed, police said Wednesday.

Galveston Police spokesman Lt. Jorge Trevino said the couple had been fighting Monday night in their home in Alvin, about 30 miles northwest of Galveston.

"I don't know if there was a history of that," he said.

By the time the child's father left with his son sometime between 5 a.m. and 5:30 a.m. Tuesday to get a car repaired, the couple was no longer arguing, Trevino said.

The mother began calling hospitals hours later after becoming concerned about the baby because the father had left with few provisions for the child.

The boy, wearing only a diaper, ended up in a grassy area Tuesday morning near Seawall Boulevard in this island city about 50 miles southeast of Houston.

A Galveston couple found the body as they drove slowly along a road looking for wildlife.

There had been initial reports that the infant might have been thrown out of a moving vehicle.

"But the location of the child and the baby seat is not consistent with a moving vehicle," Trevino said. "It was likely the car was stopped."

The infant was in the car seat when it was tossed and the child was apparently ejected when the seat hit the ground, Trevino said.

A nationwide search is being conducted for the father, who dyed his hair blonde before the infant's death.

The discovery of the baby's body comes just three months after a fisherman found the remains of a 2-year-old girl in a plastic box that had washed ashore in Galveston Bay. That child, dubbed "Baby Grace," was later identified as Riley Ann Sawyers of Spring.

Riley's mother and stepfather are charged with capital murder in her beating death.

Click here for more on this story from MyFoxHouston.com.

The Associated Press contributed to this report.