Shortly after midnight on April 19, 2019, the signal abruptly went out on Gerald Corrigan’s television.

The retired college lecturer got up and went outside to fuss with his satellite dish, which was affixed to the side of his weather-beaten stone cottage in a remote part of Wales. All of a sudden, an arrow with razor-sharp edges silently sliced through the darkness. It entered Corrigan’s torso, puncturing the 74-year-old’s internal organs. Corrigan’s longtime partner, who had been sleeping upstairs, woke up to the sound of his panicked screams.

Terence Whall “believed he had planned and committed the perfect murder,” Detective Chief Inspector Brian Kearney of the North Wales Police told reporters on Monday. According to authorities, the 39-year-old sports therapist and tai chi instructor tampered with Corrigan’s satellite dish, then hid in a darkened field and aimed a crossbow at the older man. Three weeks later, Corrigan died of sepsis.

“There was no forensic evidence, no direct eyewitness evidence to the shooting,” Kearney said, according to the BBC. “And, in fact, no one saw him going to and from the scene.”

But months later, a burned-out Land Rover found in an abandoned quarry led investigators to Whall. On Monday he was found guilty of murder and conspiring to pervert the course of justice in what authorities described as a “barbaric medieval-style execution”

The exact motive behind the slaying remains a mystery. A bespectacled, white-bearded man, Corrigan was “just an average bloke enjoying his retirement,” his daughter, Fiona, told reporters on Monday. “He enjoyed a lie in, a nice cup of tea and reading books. He loved Laurel and Hardy films and photographing flowers and mountains. Our lives won’t be the same without him.”

According to the Barrhead News, Corrigan had retired from teaching photography and videography about 20 years earlier and was a full-time caregiver for his partner, Marie Bailey, who has multiple sclerosis. The two lived in a rustic farmhouse surrounded by stone walls and grazing cows in Anglesey, an island off the rugged coast of Wales that Corrigan had chosen for its birdwatching opportunities.

After the crossbow attack, Bailey told police that she and her partner were usually a “boring couple” who kept to themselves, but that in recent years they had gotten mixed up with a man named Richard Wyn Lewis. The couple allowed Lewis to use one of their outbuildings to grow a small amount of cannabis, which helped with Bailey’s MS symptoms, North Wales Live reported. But when Corrigan discovered Lewis was cultivating far more plants than he’d agreed to, he grew angry and confronted the man.

Lewis had previously been convicted of fraud, and, according to the BBC, he owed Bailey and Corrigan a shockingly large amount of money. Thinking that they were investing in real estate development projects, the couple had reportedly given him about 250,000 pounds, the equivalent of more than $324,000. But after a year and a half, Bailey and Corrigan hadn’t seen the returns that they’d expected. In the weeks leading up to the crossbow attack, they told Lewis their money had run out.

According to the Barrhead News, Lewis is still under investigation. But prosecutors haven’t been able to say with certainty that his troubled relationship with Corrigan had anything to do with the man’s murder.

Instead, investigators honed in on Whall after finding the Land Rover Discovery in a deserted quarry on June 3, 2019. The car had been set on fire, but its sophisticated GPS system had recorded all of his travels, down to when the engine turned on and when the doors opened and closed. According to the BBC, the “black box” showed that Whall had been near Corrigan’s home on the night of the attack and scoped out the area the night before.

Whall, who had been seen practicing shooting a crossbow, was arrested on June 25. He insisted he had never met Corrigan, and has repeatedly denied any involvement in the murder. After initially lying to police and saying he was home when the attack took place, he changed his story and claimed he’d been having open-air sex with a friend near Corrigan’s house, but hadn’t wanted anyone to know. The previous night, he said, he had driven by while looking for a cliff where he could meditate.

But the man who was supposed to provide Whall’s alibi testified they hadn’t been together on the night of the crossbow attack and their relationship had never been sexual.

Other pieces of evidence pointed to the 39-year-old. The arrow that killed Corrigan was made of a 20-inch fiberglass shaft topped with a bright green bladed broadhead, North Wales Live reported. According to prosecutors, only two people in the United Kingdom had purchased that exact same combination from Amazon in the year leading up to Corrigan’s death. One had been planning a hunting trip to South Africa. The other was Whall.

And Whall was also somehow connected to Lewis, who had a tangled financial relationship with Corrigan. After the retired professor’s death, Whall made repeat visits to Lewis’s home — often in the dead of night, prosecutors said. According to Sky News, he placed a tracker on Lewis’s car. And in May, Whall and a friend were arrested at Lewis’s house after a dispute over money.

The friend, 36-year-old Gavin Jones, also helped set the Land Rover ablaze and was found guilty of conspiring to pervert the course of justice and arson of a motor vehicle on Monday, authorities said. Two other men, Darren Jones, 41, and Martin Roberts, 34, had previously pleaded guilty to arson. All four defendants are slated to be sentenced on Friday.

During Whall’s trial, prosecutor Peter Rouch told jurors the shooter’s apparent link to Lewis “may be of significance,” the Guardian reported. But he also warned there might never be a clear explanation for why Corrigan was shot down in such a brutal way.

“The injuries caused by a crossbow are not designed just to kill, they are designed to mutilate,” Fiona Corrigan told reporters after the verdict was announced Monday. “The particular weapon is designed for hunting to bring down game, and that is what my dad became: prey. We may never know why.”