A severed head has been found in a quarry in Cambridgeshire - and police believe it may belong to a man who was hit by a train.
The victim whose severed head was found in a quarry was a man aged between 30 and 50 who could have been hit by a train in a "tragic accident", according to police.
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Officers believe that the head could have been lodged in a nearby bridge for more than a decade before coming loose when the structure was cleaned.
Experts from the Natural History Museum and forensic dentists have been working with police to determine who the person was and when they died through specialist testing.
It is thought the victim was a man aged 30 to 50 who may have met his death as long ago as the 1960s but more likely around 10 years ago.
Detective Inspector Jerry Waite said: "One possible scenario we are looking at is that it may have been a tragic accident whereby the man was hit by a train along the Bedfordshire line.
"We believe the head may have been lodged somewhere along the structure of the bridge in Sharnbrook, and as part of the recent cleaning process, has been dislodged, found its way into the skip and deposited at the quarry in Mepal.
"We have been working very closely with anthropologists at the Natural History Museum in London to establish the age and gender of the deceased, as well as the National Crime Agency's Missing Persons Database, which unfortunately has not shown any DNA matches.
"I would urge anyone who has any suspicions around who this person may be to contact us."
A post-mortem examination was unable to determine the cause of death after a worker at the site in Mepal, Cambridgeshire, made the gruesome discovery on May 16.
Anyone with information is asked to call the Major Crime Unit on 101 or Crimestoppers anonymously on 0800 555 111.