An animal rights group which sent letters saying they had the remains of a pensioner's body that was stolen from a church graveyard should prove their claims, detectives said today.

Staffordshire Police are following up an offer made by activists to return part of the remains of grandmother Gladys Hammond, whose body was snatched from St Peter's Church, in the village of Yoxall, last October.

The macabre offer was made in a chilling letter last week by a group calling itself the Animal Rights Militia.

Detective Chief Inspector Nick Baker, leading the investigation, made an appeal on BBC1's Crimewatch programme last month after letters were received from people claiming to have her body.

In a statement, Mr Baker said they recognised the significance of the letters and asked the authors to authenticate their claims.

But he added: "In the letters, they now say they have co-ordinates for where they've put part of Mrs Hammond's body but, a week since their last contact, they're choosing to stay quiet.

"We are asking them to prove what they say is true by giving us the exact location."

The Burton Mail, which received one of the letters, reported that the author had used a codename and issued a threat to Mrs Hammond's relatives, who run a guinea pig breeding farm at Newchurch, Staffordshire.

Mrs Hammond, who was 82 when she died in 1997, was the mother-in-law of a partner in the breeding farm business.