The body of a 4-year-old boy missing for three days was found in a wooded area about 25 miles south of his home on Saturday, and his step-grandmother was arrested and charged with murder after she led police to the site, authorities said.

Matel Zachery Sanchez (search) was reported missing from his home in the Portland suburb of Milwaukie on Wednesday afternoon.

Police initially assumed the child had gone on an outing with Christine Coffman (search), 43, the mother of the child's stepfather. When she returned home three hours after the child was reported missing, police began to question her, Officer Kevin Krebs said.

Police did not immediately say how the boy died but a medical investigator determined the cause of death was homicide.

"There is no indication that this was an accident," Krebs said, but he declined to give any details on how the boy died.

Coffman was arrested Saturday and was being held at the Clackamas County (search) Jail without bail. Police had impounded her car two day earlier.

About 70 people, including FBI agents, had searched for the boy after he was reported missing. Dogs and an Oregon Army National Guard helicopter also were used in the search.