FEDERAL WAY, Wash. -- Police have arrested the father of the 7-month-old baby who burned to death after falling into a fire pit.

Investigators took the boy's father, 37-year-old Alberto Rios, in for further questioning Tuesday afternoon, then later placed him under arrest at 4:45 p.m.

Rios was to be booked into the King County Jail under investigation of manslaughter.

Rios initially told police he had fallen asleep in the back yard bench Saturday night with his baby son lying on his chest. When he woke up, the child was missing.

He said he went inside to ask his wife if she had the baby, and when they returned to the yard they found the boy covered with burns in the fire pit at the house in the 2600 block of SW 333rd Place.

Neighbors rushed over when they heard screams, but it was too late to save the boy.

Neighbor Levi Thomas said the baby's name was Diego.

"He was your typical 6-month-old, all smiles and coos, vibrant and young, waiting for a chance to grow," he said.

The baby's mother is said to be heartbroken and angry over her son's death.

"She is just everything right now, everything. I can't blame her," said Sonya Squires, a friend.

Police believe the baby's death may have been a horrible accident, but were running blood tests on Rios for traces of drugs and alcohol. The results were not expected for several days.

Detectives were also questioning neighbors.

"We're trying to talk to anyone who would have been at the house in the previous 24 hours, even," said police spokesperson Cathy Schrock. "We're talking to everyone to try to put together a timeline as to what led up to this tragic incident."

A social worker contacted the baby's mother, who said she is willing to work on a safety program to keep her 4-year-old daughter safe.