Police abandoned a murder inquiry - which began at noon when Damian Williams's body was found - after a pathologist discovered "features consistent with death from hypothermia" and ruled there were "no suspicious circumstances".
Damian, of Aubrey Street, Middlesbrough, disappeared after telling his mother Patricia, 25, he was going out to build a snowman on Saturday morning. She reported him missing at 2pm. The body was discovered by a police search team in the yard of a derelict house in Egerton Street, 200 yards from his home.
Superintendent Maurice Jones told a news conference that the possibility that Damian might have fallen, become unconscious and died as a result of the cold weather could not be ruled out.
Another theory being considered was that the boy got into the yard, then found himself unable to reach the gate latch to let himself out. The walls of the yard are more than 6ft high.
A police spokeswoman said: "This has been a tragic incident and our deepest sympathies go out to Damian's family.
"We will still be carrying out some inquiries in order to complete a report for the coroner."
Police were unable to say how Damian came to be in the yard behind the boarded-up terraced house, but pointed out the gate, which was closed, was not locked.
Supt Jones told the news conference that Damian was a lively boy who knew the area well and he was known to play in and around derelict buildings. He was reported missing once before, but turned up as police were about to launch a full-scale search.
Damian's mother is separated from the boy's father, Edward Bunney, who is believed to live at Whitby, North Yorkshire. She has two older sons and a younger daughter.Reuse content