The case has featured this week in A Family Vendetta, an episode of 24 Hours In Police Custody that aired on Monday and Tuesday on Channel 4.
Josh, 32, who was a former partner of Alderton’s daughter, was shot twice in the hall of his home in Bluntisham, near Huntingdon, on the evening of 29 March 2023.
Police said that 31 minutes later, Alderton shot Gary, 57, three times at his home in Sutton, near Ely.
The Channel 4 documentary followed the case from the time the first emergency call was received, and included the arrest of Alderton by armed officers on the M5 near Worcester the following day.
Alderton pleaded guilty to both murders.
At his trial, prosecutor Peter Gair said Alderton had a shotgun licence and lawfully held a Beretta, which was used in both killings.
Mr Gair also said “it’s clear that the events were triggered by an ongoing family court case” involving Alderton’s grandson.
The court heard a victim impact statement from Gary’s mother, in which she said: “Both were killed in the most vicious, cowardly way with no opportunity for self-defence.”
In a letter to the court, Alderton wrote he was “not the person that this conflict and the family courts have driven me to become”.
He added: “If I could turn back time, I would.”
He was jailed for life, with a minimum term of 25 years.
