Investigators in the West German town of Grevenbroich have started DNA tests on hundreds of men in the hope of solving a 23-year-old murder cold case.

Claudia Ruf, 11, was found sexually assaulted and murdered 70km (43 miles) south of the town in 1996. No one has been charged with her death.

Police sent invitations to at least 900 men in an effort to match DNA samples recovered from the scene.

The first day of testing started at 10:00 (09:00 GMT) on Saturday.

Those who agreed had saliva swabs taken at a local primary school, where the samples were being collected.

Claudia Ruf was kidnapped in May 1996 while walking a neighbour's dog in Grevenbroich, which is about 40km north-west of Cologne.

Her body was found two days later having been strangled, doused in petrol and partially burned.

Hiding 'far too long'

Claudia's father, Friedhelm Ruf, made an emotional appeal in a video message last week.

"After more than 23 years, there's a big possibility to solve the sad fate of my daughter," he was quoted by AP as saying. "The perpetrator has been able for too long to hide behind all of us."

A police spokesman told Bild newspaper that there had been a lot of interest in their renewed effort to solve the case, including dozens of tips.

Men aged over 14 at the time of her death have been invited to take part in the DNA testing. (BBC)