A member of The Master Locksmith Association claims a key found in the garden of the man accused of two double murders in Pembrokeshire fitted a lock in a farmhouse which belonged to one of his alleged victims.

Swansea Crown Court heard today the key was discovered at 66-year-old John Cooper’s former home at St Mary’s Park, Jordanston, near Milford Haven in 1998 by police investigating a string of burglaries he was later jailed for.

Detectives found it fitted a lock in a bedroom door at Norton Farmhouse which once belonged to millionaire farmer Richard Thomas.

Cooper is accused of using a shotgun to blast to death Mr Thomas, 58, and his sister Helen 54, at their three storey manor house in Scoveston Park Farm, Pembrokeshire, in 1985 which was then set ablaze.

Giving evidence today master locksmith John Crummock said the key fitted the lock at Norton Farmhouse “like a glove”.

He said it was not the original key but he was “one hundred per cent certain” it had been used in the door over a long period because grooves on it were created by the inner workings of the lock which he examined in detail.

He was challenged by Mark Evans QC, for Cooper, and agreed that many keys could have opened the lock which was of basic and a very common design.

Cooper, now a grandfather, is also accused of gunning down Oxfordshire holidaymakers Peter and Gwenda Dixon on the Pembrokeshire Coastal Path at Little Haven four years later.

Cooper denies the four murders plus charges of rape, indecent assault and attempted robbery related to an alleged attack on five teenagers at the Mount Estate, Milford Haven in 1996.

The case continues.