Boyer was arrested after a woodland search

Robert Boyer, 43, was accused of killing father-of-three Keith Frogson before setting fire to his house in Annesley Woodhouse, Nottinghamshire.

He was arrested in woodland and charged with murder weeks after the 62-year-old was killed in July 2004.

The court was told Boyer shot his victim with a crossbow and then hacked him to death with a sword.

On Wednesday Boyer also admitted setting fire to the grandfather's home in Bentinck Street almost two weeks after the killing.

Woodland hideaway

The court heard that the 43-year-old was fixated on Mr Frogson, wrongly believing he was persecuting him and trying to destroy his home.

Andrew Easteal, prosecuting, told the court: "The defendant shot Keith Frogson first of all with a crossbow, then struck him repeatedly with a sword until it was clear that he was dead.

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"He had convinced himself that Keith Frogson was trying to dismantle his house brick by brick, that acid was being thrown at the brickwork and that a screwdriver had been used to chip away at the bricks."

A spokesman for Nottinghamshire Crown Prosecution Service added: "This was an awful crime and police are to be congratulated on their thorough and painstaking investigation.

"It was only after very careful consideration and consultation that the prosecution team decided that the evidence of Boyer's mental condition was such that a charge of murder was not sustainable."

During the 1984/85 miners' strike Boyer crossed picket lines while Mr Frogson remained loyal to the National Union of Mineworkers.

Psychiatric reports

But Mr Frogson's family has told the BBC there was no animosity between the two over the strike.

Detectives arrested Boyer in August 2004 after finding his hiding place in Annesley Woods in Nottinghamshire.

The hideout was "well constructed" with a cover made of branches and leaves, police said after his arrest.

Det Ch Insp Russ Foster said Boyer had survived for up to four weeks on tinned food and bottled water.

Mr Justice Pitchers adjourned the case for 12 weeks for further psychiatric reports and to allow experts to assess Boyer at Rampton Hospital in north Nottinghamshire.