A man was arrested today over the murder of a pensioner who was stabbed after going to the aid of his neighbour - a convicted paedophile - during a robbery.
After the death of Graham Buck on Saturday, Hertfordshire Police appealed for help in tracing 55-year-old Ian John McLoughlin who they wanted to question in connection with the stabbing.
McLoughlin, also known as Ian John Baker, was arrested in London at around 1am and is being questioned on suspicion of murder and robbery, the force said.
Mr Buck, 66, received fatal stab wounds when he responded to cries from the home of 86-year-old Francis Cory-Wright in the village of Little Gaddesden, near Berkhamsted.
McLouglin was on day release from Springhill prison in Aylesbury, Buckinghamshire, after being convicted in 1992 and sentenced to life imprisonment for the murder of 56-year-old Peter Halls, from Brighton.
McLoughlin was 22 years into a 25-year sentence, according to police, and was serving his sentence at Springhill.
He was also jailed for manslaughter in 1983 following the death of 49-year-old Len Delgatty, from Stoke Newington, north London. He was sentenced to 10 years for this offence which was later reduced to eight years on appeal.
Police said Mr Buck, who lived two doors away from Mr Cory-Wright, went to help Mr Cory-Wright after hearing shouting in his front garden.
Mr Cory-Wright was jailed for 30 months in 2011 for indecently assaulting a 10-year old boy in the 1970s. Mr Buck, a father-of-three and grandfather, and Mr Cory-Wright are not believed to be connected in any other way than being neighbours.
Detective Chief Superintendent Jeff Hill said Mr Buck, described as a retired financial industry worker, paid the "ultimate price" for intervening during the robbery at the home of an elderly neighbour.
Mr Buck leaves behind a wife, two sons and a daughter, two grandchildren and a former wife.
In a statement police described him as a devoted husband, father and grandfather who "appreciated his life, getting great satisfaction from his family being happy and healthy".
"He was a man who would help anyone in need, with a strong sense of doing the right thing," it said.
An earlier statement from Mr Buck's family said: "We have no words to express how much Graham will be missed. We were all in such a happy place as a family. We were all so settled, with growing numbers of grandchildren whom he adored being around.
"We haven't seen him happier than being around his grandchildren, he was so proud. We cannot get over that we have lost him.
"He's going to be missed by so many people."