Brian Low was walking his dog on a remote country path when he was shot dead by a former colleague whose hatred had festered for years.

The 65-year-old was found near Aberfeldy in Highland Perthshire with blood on his hands and face – but police did not realise at first that he had been murdered.

The former groundsman’s death was not treated as suspicious for several days, until a post-mortem confirmed he had died from gunshot wounds. Shotgun pellets had fallen from the body bag before his body was examined.

It was another three months before the killer, retired gamekeeper David Campbell, was arrested.

He is now serving life for murder – but Brian Low’s family still cannot understand the mistakes which were made after his body was found.

They have spoken publicly for the first time in two-part BBC documentary Murder Trial: Death of a Dog Walker, which follows the police investigation and the trial.

“I was so angry and so sad at the same time,” says his brother Douglas Low.

“How could this happen?”

Brian Low’s body was discovered on Leafy Lane, with his dog Millie by his side, on the morning of 17 February 2024.

One of the first detectives on the scene told the murder trial that he believed Low’s injuries were consistent with him falling while out for a walk.

The court was shown graphic photographs of Low’s body lying on the path. His face was covered in blood and black marks.

Douglas Low said the pictures were “so horrific I barely kept my breakfast down. I can’t imagine why someone would say that’s a medical event”.

Brian’s niece, Jacqui Low, added: “It just seems incredible that they didn’t see the marks on his face, the shot.”

The post-mortem found that Low’s clothes were peppered with holes and he had sustained about 30 pellet injuries.

The delays meant that a cordon at the crime scene was not put in place until 23 February, six days after Low’s body was found.

Det Ch Insp Martin MacDougall, of the Major Investigation Team, said: “When you have that delay, a number of things go through your mind of what we could potentially have lost evidentially.

“Footprints in the soil, tyre tracks, CCTV.”

The murder inquiry was finally launched 10 days after Low’s body was discovered.

A press conference took place a few days later, where MacDougall and colleague Cdr Greg Burns were grilled over the blunder.

One detective told the filmmakers that there had been a lot of media interest and admitted: “We’re kind of a wee bit on the back foot”.

Over the next three months police spoke to 800 witnesses and trawled through 2,400 hours of CCTV footage from 56 cameras.

The documentary followed prosecutor Greg Farrell as his team built the case against Campbell, as well as the accused’s lawyer, Tony Lenehan KC, as he attempted to dismantle the prosecution’s timeline and cast doubt on the evidence.

Because of the potential missed forensic opportunities, the prosecution led a circumstantial case during the trial.

It linked smaller strands of evidence to build a picture of Campbell’s decades-old grudge against Low, who had worked at the nearby Edradynate Estate with his future killer for more than 20 years.

Campbell had been the head gamekeeper at the estate.

He was described by local farmer Sally Crystal as “highly respected” and a man who “ran a very, very good shoot”.

Crystal had first met Campbell during the 1987 shooting season.

She said that when he first arrived he had been an excellent gamekeeper – but as his reputation grew, he became “very arrogant”.

“David started really misbehaving, the family (who ran Edradynate) started mistrusting him,” said Crystal.

Asked during the trial how the two men got along, she said: “At first it wasn’t noticeable, but as time went on there was a coldness.

“On at least one occasion I had been talking to Brian in the morning and David walked past me.

“He turned to me, angry because I was slightly late that morning and I’d still had time to talk to Brian.

“He walked away and he said I (expletive) loathe that man. I hate him.”

Pam Curran, who was Low’s partner for 22 years, said everyone who met Brian liked him.

“I don’t think he had a bad bone in his body,” she said.

Douglas Low said he had not thought that his brother had an enemy in the world.

“Who would want to harm Brian? He was the nicest, kindest person you could ever imagine,” he said.

“It’s just so unbelievable.”

However, the trial was told of bad blood between the two men.

Campbell had suspected Low of “planting” items which were allegedly found during a raid on his then-home on the estate after alleged bird poisonings.

Campbell said he had not had any contact with Low since 2017 and that he did not know he had left Edradynate Estate until he saw it on television.

Pam Curran said: “I knew they had a fall-out, a serious one because Dave was being investigated for poisoning birds of prey and it had happened more than once.

“And whatever Brian had said to the police really angered Dave and they had a right set-to.

“Brian wouldn’t tell me the ins and outs of it, but I knew it was bad. Brian was really upset by it.”

Campbell was removed from Edradynate in early 2017 having worked there for more than 30 years.

During the trial, defence advocate Lenehan noted that in the seven years since he had left the estate both men had lived near each other without there being any issue.

But in reality, Campbell had been planning how to kill Low – and cover his tracks.

On the morning of Friday 16 February 2024, Campbell set to work on his plan.

He covered the CCTV camera at the rear of his home with duct tape in the morning, not removing it until that evening.

A figure the prosecution said was Campbell was seen on CCTV riding through Aberfeldy on a distinctive bicycle, heading in the direction of the murder scene.

One witness told the trial that Campbell had later asked a bike repair shop to change the tyres.

The police also saw CCTV footage from a nearby farm showing a “spooked ” horse running around a field, at the same time Low was believed to have been shot.

Officers say the time matched the last known activity from Low’s mobile phone.

Three months after the killing, police finally arrested Campbell.

He was on the toilet naked when officers arrived at his home.

In a combative police interview, Campbell was asked by arresting officer Det Con David Budd if Low’s death had been an accident.

“I don’t know,” he replied.

Budd asked him: “Well did you mean to shoot him or not?” – to which Campbell replied: “Cheeky bastard.”

He went on to say that he “100%” did not have anything to do with Brian Low’s death.

Campbell gave evidence in his own defence during the trial.

He said he spent most of the day in his house and made a lengthy call to the local council about a planning application.

Campbell said he did not ask for a solicitor after his arrest because he “didn’t need one” and denied having anything to do with Low’s death.

However, he was found guilty of murder after a 15-day trial at the High Court in Glasgow. The jury delivered its verdict after three days of deliberations.

Judge Lord Scott told Campbell his “targeted assassination” had been “an appalling and senseless act of extreme wickedness.”

He was jailed for life and ordered to serve a minimum of 19 years before he can apply for parole.

Pam Curran said she had not been able to go into court for the verdict because she did not know how she would react.

“That one act of violence has changed so many people’s lives, and for what?

“An argument over something on an estate that happened years ago.”

She said her life would never be the same.

“I’m not getting to see Brian ever again. How is that right?”

“But you can’t feel sorry for yourself.

“You just have to pick yourself up and keep going, because that’s what he would have wanted.”