Murdered David Alderson 'hit with spanner and drowned'
A man was hit over the back of the head with a large spanner before his killer drowned him in a pond, a court has heard.
David Alderson, 72, was found face down in a pond at a disused mine near Bissoe, Cornwall, in January 2014.
Kevin Cooper, of Poldory Way, Carharrack, and Trewen Kevern of Tresillian Road, Falmouth, deny the murder.
Mr Cooper told Truro Crown Court he saw Mr Kevern kill Mr Alderson.
He told the court Mr Kevern had arranged to meet gun enthusiast Mr Alderson at Wheal Maid mine to buy a handgun on the evening of 17 January 2014.
He said he was asked to go along as "muscle to make sure it all went ok" but knew no details about the gun deal.
Mr Cooper said he went looking for the two men when they didn't return from their meeting as he had expected.
He said he found them next to a pond where he saw Mr Kevern hit Mr Alderson over the back of the head with a large spanner.
Mr Cooper told the jury Mr Alderson "fell flat on his face and then Mr Kevern put his foot on the back of (Mr Alderson's) head while his face was in the water".
He said he didn't intervene because he feared he "might be next", adding: "I know what sort of a temper he's got and he had a spanner of that size in his hands."
Asked by his barrister Andrew Jefferies QC what state he thought Mr Alderson was in when they left the scene, he replied: "Put it this way, he wasn't moving."
Earlier the court heard Mr Alderson legally kept an arsenal of weapons, ammunition and gunpowder along with about £40,000 cash in two safes within his Falmouth flat.
The retrial continues.