Early one September morning in 2023, two men arrived at an ancient Roman wall in northern England and under the cover of a storm committed one of Britain’s most notorious recent crimes.

They cut down a tree, prosecutors allege in a case that has gripped the U.K.

Framed perfectly by two small hills along the nearly 2,000-year-old fortification, the giant sycamore had become a tourist attraction and a regional symbol. It even played a scene-stealing role in the 1991 film “Robin Hood: Prince of Thieves” with Kevin Costner. The tree’s demise sent shock waves through Britain, triggering accusations and acrimony locally and a major criminal investigation that had police crisscrossing England examining chain saws.

At a courtroom in Newcastle, Adam Carruthers, 32, and Daniel Graham, 39, are now accused of causing criminal damage to the tree and the ancient wall, a Unesco World Heritage site, it fell onto. They have both pleaded innocent.

The deliberate destruction of old trees has often stoked anger around the world. In Britain, where trees have starring roles in royal and scientific history, there were few as loved as this giant sycamore, under whose broad canopy people had married, spread ashes or just got drunk.

But just after midnight on Sept. 28, the over 150-year-old icon was felled in less than three minutes.

Prosecutors say the journey to its demise began the night before, when Carruthers and Graham loaded a chain saw into a Range Rover and drove 25 miles from their hometown of Carlisle in a trip later tracked through mobile-phone data and police cameras.

“Having completed their moronic mission, the pair got back into the Range Rover and traveled back towards Carlisle,” prosecutor Richard Wright told the court, which began hearing the case this week.

On that journey home, Carruthers’ partner sent him a video of a child being bottle fed, according to a text exchange that prosecutors presented to the court. Carruthers responded, “I’ve got a better video than that.” He later sent footage of what prosecutors say is the tree being cut down.

VIDEO: Footage of what prosecutors say is the tree felling, digitally enhanced and shown in court, was released by the U.K.’s Crown Prosecution Service.

Watching that footage played on the BBC’s live coverage of the trial Wednesday, Alison Hawkins felt emotional.

Hawkins had wanted to visit the tree since seeing it as a child in “Robin Hood.” Instead, the hiker and her husband were the first to witness its dismembered trunk.

When Hawkins arrived at the site that morning, she assumed a strong storm the previous night had brought it down. But then a park ranger showed up and pointed to a silver line sprayed on the trunk to guide a chain saw. She and her husband were brought to tears.

“You can forgive nature, you can’t forgive that,” she said.

News of the felling soon spread on social media. It led U.K. media bulletins and websites throughout the day. As people flocked to the crime scene, already taped off by police, the tree was removed to stop souvenir hunters from taking a piece.

Carruthers and Graham appeared to be reveling in their feat, prosecutors said.

“It’s gone viral. It is worldwide,” Graham said in a recorded message to Carruthers as they swapped news stories, according to a copy of the recording sent out by the prosecution.

But the pair weren’t happy about all the coverage. Spotting a comment on Facebook calling the felling a disgusting act committed by weak people, Graham left his alleged accomplice another voice note. “Weak? Does he realize how heavy sh– is,” he said.

Meanwhile, some locals were taking the law into their own hands.

Over a hundred people called a nearby pub, the Twice Brewed Inn, after it promised a £1,200 bar tab, or about $1,500 at the time, for any information leading to a conviction.

“The phone was going all the time, with people calling saying I think it is this person, it is that person,” said Steve Blair, the landlord, whose pub sells a beer named Sycamore Gap after the tree.

The police soon arrested Walter Renwick, a retired local lumberjack who had recently been evicted from the farm that his family had leased for generations. Renwick was released shortly after but said the arrest had made him a pariah. The former farmer took to wearing a Rod Stewart-style blond wig to hide, he told the Sunday Times newspaper.

“If I’d have done a murder, I’d be getting less hassle,” he said.

By October, police had new suspects and arrested Carruthers and Graham.

Soon after the arrests were announced, a different Daniel Graham, a local forestry worker, was at work when he got the first of what would be over 400 calls, texts and Facebook messages angrily accusing him of destroying the tree. Amateur detectives had found him online next to pictures of newly felled trees and jumped to the wrong conclusion.

“They were swearing and saying terrible things about how dare you and how disrespectful to cut down that tree,” he said.

Graham is keeping tabs on the trial of his namesake. U.K. websites have run live blogs of the packed-out court proceedings, while broadcast news featured regular updates.

After arresting Graham and Carruthers, police got to work, sifting through their phones and that of Carruthers’ partner.

Among the evidence: a photo and videos taken of the Range Rover’s trunk showing what prosecutors say is a trophy section of the tree plus the chain saw that cut it down.

Examining the photo, a forensic botanist concluded there is strong evidence to believe that section of wood was from the sycamore.

Police never found the weapon. The other unsolved mystery: the motive for the crime.

Cutting down or damaging iconic trees often provokes strong reactions.

Anger over the felling of the giant “Discovery” redwood tree in California helped push the U.S. government in 1864 to set aside land for preservation for the first time. In 2020, Britain was scandalized when a 3-foot chunk of the centuries-old oak tree where the actual Robin Hood, as opposed to Costner, was by legend supposed to have hidden was snapped off by people climbing it.

The outpouring of grief over the sycamore, aided by social media, has perhaps surpassed them all. George Mahood, a writer based in southern England, said he felt physically sick when he heard of the tree’s fate.

Mahood, who used a picture of the sycamore for one of his books, said its attraction came from its setting. Nobody would have cared for the tree had it been just one of many there, he believes.

“It was like it was a perfect fit for where it grew,” he said.

At the Twice Brewed Inn, less than half a mile from where the tree’s stump now stands, a TV screen broadcast news of the trial.

“Everyone in the pub is turning to the screen when it comes on,” Blair said.

Blair found it uncomfortable to watch footage of the felling. “It was just a tree,” he said. “But without breaking into bad language, it makes us feel sick…it’s devastating to see.”

What remained of the sycamore has since been chopped up, with pieces distributed to sites including a local visitor’s center. The pub is set to receive its own slice, which Blair plans to put under the floor with a glass panel over it.

Write to Alistair MacDonald at Alistair.Macdonald@wsj.com