The discovery was made by a workman clearing vegetation
A bag containing what are thought to be human bones has been found at the side of the M5 north of Bristol.
A motorway workman clearing vegetation next to a slip-road made the discovery at junction 14, near Thornbury, South Gloucestershire, just after 1200 BST.
Det Insp Richard Budd said the workers had found what are believed to be human body parts, including a skull.
"We don't know what we are dealing with... this could be someone's son, daughter, husband or wife."
"We've attended with our specialist teams and investigations are continuing into how it [the bag] got there," the officer said.
"It's a delicate scene, we don't know what we are dealing with.
"There are a number of experts I want to get to the scene to give us the best possible options of identifying who this is and how long they've been there.
"We have to do the best job for anyone who may be related.
"There is still a lot of work that need to be done to excavate the remains, some of them are partially buried. It's obviously been there for some time."
One lane of the slip-road for junction 14 remains closed.