Albuquerque police are trying to unravel the mystery of how the unidentified body of a small boy wound up buried in an Albuquerque playground after a preliminary autopsy provided no clues about how the child died.

"There were no obvious signs or cause of death," Albuquerque police spokesman John Walsh said Saturday after receiving the results of a preliminary autopsy from the state Office of the Medical Investigator.

Saddened neighbors made a makeshift memorial of stuffed teddy bears, toy trucks and flowers at the base of the playground equipment at Alvarado Park in northeast Albuquerque and planned to hold a candlelit memorial for the boy in the park Saturday night.

About 50 police investigators who went door-to-door Saturday asking neighbors for help in identifying the 3- to 5-year-old boy also came up empty-handed, Walsh said.

"No one has stepped forward as parent, guardian or caretaker or any other relationship with this child," Walsh said. "Anybody who has seen or heard of any, anything, involving a child in that area, we want them to call us."

The officers fanned out into neighborhoods farther from the park where the body was found Friday afternoon. A mother there with her children spotted a shoe sticking out of the sand and called police after making the grim discovery.

The 38-pound boy was wearing a red shirt with the image of a four-wheel drive truck on the front, black nylon pants with red stripes and black shoes. He had short straight black hair and was 3-feet, 2 inches in height, according to Walsh.

Walsh said the preliminary autopsy determine the child was either "Native American or Hispanic."

"First we have to concentrate on the identification. Two, we're trying to determine the cause of death and, three, we're trying to find who might have been responsible for this child," Walsh said.

OMI will conduct blood and toxicology tests and more advanced pathology techniques to find out more about what happened to the boy and try to identify him. Walsh did not know when the results of those tests would be available.

Initially police thought the boy was from the neighborhood near the park, but Walsh said they also have checked for possible victims in other states.

Police found a woman who was seen at the park Thursday with her children, but she did not know anything about the boy.

Albuquerque Police Chief Ray Schultz said Friday the case was unique because his department has not had any reports of missing children in the 24 hours before the body's discovery.

Forensic experts who exhumed the body told police that the boy could not have been dead longer than 48 hours, Walsh said.

Neighbors were tearful as they spoke of the tragedy.

"You just want to cry about something like that," neighbor John Bell told Albuquerque television station KOAT.