Human remains found in a park could be from someone killed more than seven years ago, police have said.
Police have been examining a site near Brackley Park in Hull after the discovery 12 days ago.
A police cordon has been expanded as forensic investigators examine a number of different sites linked to body parts.
Hull Live reported that one theory being considered by officers is that the victim may have been struck a train from the nearby railway line.
However, police believe the person may have died more than seven years ago. It is not known if police have been able to identify the victim.
The investigation is being led by British Transport Police because of the proximity to the railway line. The land to the west of Brackley Park is owned by Network Rail.
Police were first called to the scene at 6pm on 7 December following "reports of human remains found".
On Friday, there were four separate crime scenes with tents behind a cordon close to the park. Crime scene investigators in white forensic overalls were seen at the site.
Investigators have had to work in cold weather, with temperatures dipping to as low as -5C at night.
The area, which has been closed off to the public, is popular with dog walkers, families and cyclists.
British Transport Police Detective Superintendent Stephen May told Yahoo News UK on Monday: "Specialist teams have been searching a single isolated area of the railway embankment near Brackley Park after human skeletal remains were found on Wednesday 7 December.
“It’s a small area of land that the public do not have access to.
“We believe they are the remains of one person and detectives await the outcome of a post-mortem examination to identify them and establish the circumstances behind their death.
“At this stage we are unable to confirm how long the bones have been there, however it is estimated to be in excess of seven years.
“A cordon will remain in place while we continue searching the area, and we would like to thank residents for their patience while we carry out our final assessments of the site.
“I understand that there has been some local concern around this incident and I would like to reassure the community that we don’t believe there is any wider risk to the public.”
A mother who lives close to the park, who only gave her name as Nicola, said: "We have lived here for 11 years and walk our dogs every day, if not twice a day, in that park.
"It comes as a shock that something like that would happen on our doorstep.
"On Wednesday afternoon, we were actually out with the dogs when we saw a person leading a police officer to that area - that must have been what it was for.
"It is a lovely place for families around here but the area has had its trouble before, especially in the summer.
"There will be kids with motorbikes being anti-social or people taking drugs now and then but, usually, it is nice and quiet."