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.
More top news
The Met Police are searching for a shotgun-wielding gang of burglars who were caught on CCTV smashing into an East London home
A senior employee at a 4-star London hotel has been jailed for six years for raping a man who he lured to a fake job interview.
Children's charity Kids Company is being investigated by the Metropolitan Police over criminal allegations.