LONDON: A British pensioner was on Friday sentenced to life in prison with a minimum of 13 years for murdering his stepson in 1968 in an attack witnessed by the toddler's brother.

David Dearlove, 71, was found guilty at Teesside Crown Court in northeast England of swinging 19-month-old Paul Booth by the ankles and bashing his head against a fireplace.

The attack was seen by Paul´s brother Peter, who was three years old at the time and had crept downstairs at the family home to get a drink.

Peter Booth told police what had happened after childhood memories came back to him in adulthood but no action was taken initially.

In 2015, after seeing a photo of Dearlove with Paul on his knee on Facebook, Booth went to the police again and an investigation was launched.

"I want to pay tribute to Paul´s family and other witnesses who provided such an emotive testimony," Detective Inspector Mark Dimelow said outside the court after the verdict.

"I praise their bravery in having to relive events from 50 years ago," he said.

Dearlove, who is retired and has two daughters, was 21 when he moved in with Carol Booth, a single mother, and her three young children. He said at the time about the death that Paul had fallen out of bed.

The couple split up in 1970 and she died in 1991.

A month before Paul was killed, nursery staff were concerned about bruises on his body and the injuries were investigated by the authorities.

The case relied mostly on that investigation, as well as a post-mortem examination, since Paul Booth was buried in an unmarked grave and his body has not been found.