The detectives were going to talk with anybody who had contact with Travis Mullis, the baby's father. The crime scene investigators were going to look for any possible evidence in Mullis' car, Trevino said.
Mullis, 21, known as "T.J.," surrendered to Philadelphia police Friday, telling them he placed the 3-month-old baby on the ground and then stomped on his head three or four times until he felt the skull collapsing, Trevino said.
"We have a pretty clear picture of what happened based on (Mullis') statements. But I can't release those details without risking hurting the case," Trevino said.
Mullis has been charged with capital murder in Galveston and his bond has been set at $1 million. He also has a felony charge out of nearby Brazoria County of enticing a child. Alvin police are investigating an allegation that Mullis took an 8-year-old girl from her bed in January, took her to a school or park and asked her to remove her pants.
Investigators still have more questions for the infant's mother, who spoke with them after the baby's body was found. But a family representative has stated she will not be talking to police after getting an attorney, Trevino said.
"We have more questions for her in order to wrap up the investigation," he said. "But she is not cooperating with that."
He said Sunday that he couldn't comment on whether she's considered a suspect.
After attending a memorial service on Saturday for her son, the woman left the church, declining to talk to the reporters.
During the service, she read from a letter she wrote to her son Alijah, the Houston Chronicle reported Sunday.
"Mommy loves you so much," she said. "Thank you so much for giving me the best three months of my life."
Neighbors of the family, who were living in a trailer with friends in Alvin, told the newspaper they had many unanswered questions about what happened.
"The same question probably thousands of people got - Why? No matter how much anger you have for somebody, you don't go to the point of doing that, especially to a baby," said neighbor James Robertson.
The couple apparently were having financial and relationship problems and often argued, said Robertson's wife, Lisa.
Trevino said the couple had argued Monday night before the infant's death but that it had not carried over to the next morning, when Mullis left with the baby.
A Galveston couple found the body Tuesday morning as they drove slowly along a road looking for wildlife. DNA tests are pending to positively identify the infant.
Galveston detectives planned to return on Tuesday.
But Mullis' return to Texas, according to Sgt. Ray Evers, a spokesman with the Philadelphia Police Department, could take several weeks, depending on whether he waives extradition during a court hearing, The Galveston County Daily News reported Sunday.
The infant's death 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.
