Police hired a specialist company to search the sewer network between the boy’s home and where he was found for clues as to how he got lost.
Joe was last seen around 6 p.m. local time on the day of his disappearance at a property near a 100 centimeters (39.3 in) diameter drain.
“Detectives therefore consider it very likely that Joe climbed into this concrete pipe while playing,” the statement said. “Now it can be assumed that Joe has increasingly lost his way in the system and could no longer find an exit.”
After he apparently climbed 23 meters along the pipe, police said he followed the sewer system through a plastic pipe only 60 centimeters (23.6 in) in diameter. Some of his clothes were found in this pipe.
The boy was able to reach the area under the manhole cover where he was found through sewer shafts and junctions.
At one point, officers launched a murder investigation after receiving a tip that the boy had been seen in the company of an unknown person, which later turned out to be false.
As for Joe, he remains in the hospital and is being treated, but has not yet been able to tell the police in detail his full story.
Andy Eckardt contributed†