Police say they have drawn a blank after a note, left pinned to a teddy bear next to a river, sparked a major search.
Police divers searched the river were the teddy was discovered
It read: "Daddy and Mummy love you always and forever... hope you understand why we did what we did. Love you my sweet little thing"
The note was found by a member of the public at Broken Scar, a beauty spot near Darlington, and handed to police.
The contents of the note led detectives from Durham Police to fear the worst.
A major air, land and river search involving 50 officers got underway, but nothing was found.
Police are now appealing for anyone who knows anything about the letter - which officers believe is genuine - to get in touch.
Life or death
Inspector Bill Bentham said: "We took [the note] very, very seriously. There was a real concern in case there was somebody in a life or death situation.
"We had to treat it as a worst case scenario then start mobilising as many resources as quickly as we could to help anyone we thought might be in trouble."
After police were alerted to the letter on Sunday, a police spotter plane, the fell rescue team and police divers were involved in the operation, but after several hours it was eventually called off.
The missing persons list was checked and neighbouring forces alerted.
Mr Bentham added: "We have drawn a big blank and what we really need now is anybody who has any information in relation to the note or the teddy bear to get in touch and put our minds at rest."