A mute, severely abused boy remained in a Boise hospital Friday as authorities continued their efforts to find out who he is and why he had been abandoned at an I-84 rest area.

Tests to determine his mental development were planned Friday, and the boy was being treated for malnutrition, scrapes, bruises and small burns over much of his body, said a spokeswoman at St. Luke's Regional Medical Center.The burns appeared to have been inflicted with lit cigarettes, spokeswoman Rita Ryan said.

"His life all along was what you and I would view as a living hell," said Dr. Thomas Cornwall, a pediatrician at St. Luke's.

The boy, believed to be 8 or 9 years old, was found by passers-by about 3:15 p.m. Wednesday in a restroom at the Blacks Creek Rest Area off I-84 southeast of Boise.

Ada County Sheriff Vaughn Killeen said he apparently was left there sometime after 2 p.m. Investigators had leads, but still no firm information on who might have abandoned the boy, or why.

"The possibilities are endless," Killeen said. "We know that he was dropped off. We know based on our experience that it was not accidental."

Cornwall said the boy probably would remain at the hospital at least until the weekend.

The doctor said the youth weighed only 44 pounds and was 15 to 20 pounds underweight. He was described as 3-feet 4-inches tall with short blond hair and blue eyes.

Killeen said he was found at the rest stop whimpering and wearing only a T-shirt, although a set of clothes were found near him in the restroom. He has not spoken since his discovery, and Cornwall said there was evidence of "developmental retardation."