A widower who shot dead his daughter’s ex-partner and her ex-partner’s father over a family court case involving his grandson has been sentenced to life in prison with a minimum term of 25 years. Stephen Alderton, 67, had written in previous text messages that he would “override any court decision” and that there was “always a plan B”, Cambridge crown court heard. The prosecutor, Peter Gair, said Alderton, a former chartered quantity surveyor, killed the two men with a Beretta shotgun on 29 March this year, two days after a family court hearing. The defendant, of no fixed address, pleaded guilty at an earlier hearing to the murders of Joshua Dunmore, 32, and his 57-year-old father, Gary Dunmore. The judge, Mark Bishop, described the murders as an “execution” and told the defendant: “You took the decision to take the law into your own hands and end the lives of two innocent men.” He said Alderton did this over his “distorted beliefs” about family court proceedings involving his grandson “following what was an interim and not final hearing on 27 March”. As Alderton was led to the cells, a relative of the two dead men swore and shouted “rot in prison”, which was followed by brief applause. Joshua and Gary Dunmore were found dead at their homes in the Cambridgeshire villages of Bluntisham and Sutton respectively, six miles (10km) apart. After Alderton was arrested hours later by armed officers on a motorway, he told police that “sometimes you have to do what you have to do even if it’s wrong in the eyes of the law”, Gair said. “We say it’s clear that the events were triggered by an ongoing family court case between this defendant’s daughter Samantha Stephen, nee Alderton, and her former partner Joshua Dunmore,” he said. “This concerned a request to move their seven-year-old child from the jurisdiction of the court by emigrating to the USA.” He said Samantha Stephen and Dunmore’s relationship ended shortly after their son was born and in 2020 she married her current partner, Paul Stephen. Gair said Paul Stephen, a US national, served with the US air force. “He was due to be redeployed back to the USA,” said Gair, and they “sought permission of the family court and Joshua opposed the application”. “There was a hearing on 27 March 2023 and it would appear [the child] wouldn’t be removed from the jurisdiction,” said Gair. Adrian Langdale KC, mitigating for Alderton, said Alderton’s wife died in December 2019. Gair said Alderton had sold his home and was living at the time of the offences in a motorhome at a site in Willingham, Cambridgeshire. He said Alderton had been “rapidly identified” as a suspect after the shootings because of the family court case and sightings of the white Peugeot. Alderton’s motorhome was picked up by police using automatic number-plate recognition cameras. He was stopped by armed police from the West Mercia force on the M5 near Worcester at about 1.30am on 30 March, police said. Langdale said the defendant wrote in a letter: “I’m not the person that this conflict and the family courts have driven me to become. I’ve never been a violent person, I do not have a criminal record. I’ve been a respectable, law-abiding citizen all my life. “What happened to me on 29 March, I do not know.”