The family of musician Kevin O'Brien, left dying after a drink and drug-fuelled street attack, today vowed to fight on after claiming they have been “cheated” of justice by the legal system.

In a statement to the Telegraph & Argus, relatives of Mr O’Brien, 31, said they were “devastated at the small sentences given to the people who unlawfully and viciously took Kevin from us”.

They now plan to join with other bereaved families to lobby for tougher sentences in such cases.

The father-of-two was fatally injured when his head struck the ground after he was punched in the face by Andrew Graham, 23.

As Mr O’Brien lay dying, Graham’s sister, Debi, 22, rifled his pockets. She and her boyfriend Dean Swan, 32, stole cans of cider, cigarettes and £5 cash from their victim.

All three defendants also robbed Mr O’Brien’s girlfriend, Claire Copperwaite, of her handbag. She suffered cuts, bruising, swelling and a dislodged tooth.

This week, at Bradford Crown Court, Andrew Graham was jailed for five years and eight months after admitting manslaughter and robbery. His sister, who pleaded guilty to theft and robbery, was imprisoned for two years and nine months, and Swan, who also admitted theft and robbery, was sentenced to two and a half years’ imprisonment.

Mr O’Brien and Miss Copperwaite were set upon in Oakworth Road, Keighley, after 1am on January 13. He died in hospital two days later.

The family statement said: “We feel cheated by the current guidelines that are used for manslaughter cases, as the Crown Prosecution expressed that manslaughter covers a vast area.

“We are the latest in a long list of families to feel that the punishment does not fit the crime, as expressed in a statement given to the court.

“Our life sentences started when Kevin died, and the pain will be with us forever. It could be only just over a year before Dean Swan and Debi Graham are released and a couple of years for Andrew Graham.

“We will continue to fight, along with many other families across the country that have lost loved ones to violent crime. How many more loved ones will be lost before the guidelines are changed and the sentences reflect the severity of the crime?”

The family thanked the police and Crown Prosecution Service for their “professional and in-depth investigation”.

Andrew Graham, of North Street, Keighley, told police he had drunk 15 cans of Carlsberg, Jack Daniels whisky and taken skunk cannabis and amphetamine.

Debi Graham and Swan, both of Acres Street, Knowle Park, Keighley, were also drug users. Debi Graham told police she was “stoned on skunk” and had drunk alcohol.

e-mail: jenny.loweth@telegraphandargus.co.uk