Eyes twinkling, David Campbell blows kisses at family members as he is led into the court dock. It is his routine throughout the 15-day murder trial.

When his wife Betty is called to give evidence in the witness box, he makes several shows of affection towards her and winks.

Behind him in the public benches, the faces of the partner and the brother of the man Campbell is accused of blasting to death with a shotgun are studies in grief.

Pam Curran and Douglas Low have been mourning the loss of Brian Low for two years and, even as damning evidence piles up against his 77-year-old suspected killer, it seems he is enjoying himself more than they are.

As footage of his police interview is played in court, Campbell can be seen chuckling at his own impertinent remark to a detective. Even after giving evidence on his own behalf and being grilled by a prosecutor over the murder he returns to the dock with a smile and cheery wave.

Only at one point in proceedings does a look of absolute horror spread over his face. It is open-mouthed astonishment at the jury’s verdict of guilty.

The dramatic denouement forms the climax of a new two-part documentary on one of Scotland’s most shocking murders of recent years.

Brian Low, 65, was executed by shotgun in rural Perthshire – an area practically devoid of violent crime – as he walked his black labrador Millie near Aberfeldy.

David Campbell laughed and smirked while sitting in the dock as he was tried for the murder of Brian Low

Murder Trial: Death of a Dog Walker, traces the Police Scotland investigation and judicial process from day one in February 2024 – and day one was a disaster.

A detective constable who was called to the spot where the dead man lay believed the blood on his face was most likely the result of a fall. He completely missed the fact his wounds were caused by dozens of shotgun pellets.

That meant it was the best part of a week before a murder hunt was launched.

Crucial days when the crime scene could have been preserved and combed over by forensics teams were lost.

The documentary also follows the agonising journeys of those who were closest to Mr Low as they watch the evidence unfold. For the first time, they speak publicly about the profound impact of his loss.

Pam Curran, the murder victim’s live-in partner for 23 years, is seen too fearful even to attend the courtroom when the verdict is due to be delivered. Emotionally drained, she sits in a witness room waiting for news.

‘I couldn’t go in for the verdict because I didn’t know how I would react,’ she says. ‘That verdict is going to change my life. It’s not going to make it better, but it could make it a hell of a lot worse.’

Douglas Low, a brother ten years Brian’s senior, is stupefied and distraught at the court testimony of the detective who failed to call in the death as suspicious. His sense of disbelief increases as pictures of Brian’s bloodied face are shown in court.

‘I must admit, I was so angry and so sad at the same time that, how could this happen?’ he says. 

‘And the graphic photographs. To be honest, they were so horrific I barely kept my breakfast down. They were really horrific. I can’t imagine why somebody would say that was a medical event.’

For him, the image of his brother’s face riddled with shotgun pellets represented not only a gross failure on the part of the police, but a personal failure too.

This was his ‘pesky’ kid brother – to whom he grew increasingly close in adulthood.

‘I remember when my father died of a stroke,’ he says. ‘As he was dying, I promised him that I would look after Mum and Brian. Obviously I didn’t do a very good job of that.’

Learning of his brother’s death – seemingly by a ‘medical event’ – was distressing enough. The later revelation that he was murdered – and detectives’ working assumption that the killer was someone he knew who remained at large – had left him shattered.

Brian Low’s death was only treated as murder a week after his body was found

Police at the scene where Brian’s body was found

‘It’s so, so unfair that there was all the plans that we had,’ he says. ‘Everything was just unfinished and just so abrupt.

‘And who would want to harm Brian? He was the, you know, the kindest, nicest person you could ever imagine.’

He adds: ‘I never thought he had an enemy in the world. I really didn’t. It’s just so unbelievable. And that set the tone for the horror story that nobody should have to endure.’

The seeds of the crime lay in the nearby Edradynate Estate for which, as gamekeeper, Campbell was the driving force in turning it into one of the top game shooting destinations in Scotland.

For 18 years of Campbell’s tenure there, Mr Low was the estate groundsman.

Sally Crystal, 77, whose farm borders the estate, tells the documentary that success went to Campbell’s head and, as his reputation grew, ‘he became very arrogant’.

‘David started really misbehaving,’ she says. ‘The family started mistrusting him and of course Brian was there all the time cutting the grass, strimming, doing everything. He was really needed and the family very much appreciated it.’

Meanwhile, the estate found itself at the centre of a string of wildlife crime investigations.

Retired wildlife detective Alan Stewart says it became the ‘worst’ in Tayside for the number of probes it attracted. Raptors, which prey on pheasants and partridges which shooting parties come to hunt, were being found poisoned.

Interviewed at his home, Mr Stewart says of Campbell: ‘He always denied it. And he was confident, he was arrogant.

‘He even had me in for a cup of coffee one day and I made sure that the coffee was out of a coffee dispenser and he was taking some of it as well.’

The suggestion in court was bad blood developed between Campbell and Mr Low because the latter was critical of his methods.

Advocate depute Greg Farrell tells the documentary: ‘David Campbell ultimately lost his job as a gamekeeper and we think the motive for murdering Brian Low was he had believed that Brian Low was responsible for that.’

Ms Curran reveals she was aware of the hostility. ‘I knew that they had a fall-out on the estate, 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. But Brian wouldn’t tell me the ins and outs of it.’ 

She adds: ‘David Campbell, his whole life was his work. When it ended, probably sooner than he wanted, he wasn’t happy. But not to the fact that I would have thought he would have killed Brian. And it is unreal to think that somebody you know is capable of doing that.’

Brian’s partner, Pam Curran, was emotional as she faced Campbell in court

In accordance with normal court procedure, Ms Curran is allowed to watch the trial unfold only after giving evidence herself.

As she takes her place in the public benches, she feels the stare from the dock.

She says: ‘I did note that when I went in, Dave immediately looked at me and I thought, you’re not going to intimidate me, Dave Campbell. So I just looked back at him and no, he’s not doing that to me because I thought, you know, it’s not me that’s on trial.’

The remote cameras in the courtroom often capture the murder accused and his victim’s bereaved partner in the same frame – one looking remorseless, indignant, at times even amused; the other overwrought.

‘You couldn’t really not look at him because he’s right in front of you,’ reflects Ms Curran. ‘And when he was getting taken down at the breaks he would wave to his granddaughter who was there.

‘And I was quite upset, thinking Brian’s family were there as well, and it did impact on them.’

The prosecution case hinged on the thesis Campbell had borrowed his wife Betty’s e-bike and ridden to a path known as Leafy Lane with a dismantled shotgun in a backpack.

There he reassembled the gun and ambushed Mr Low when he walked by with his dog.

CCTV cameras in Aberfeldy yielded images of a figure on an e-bike with a backpack but Campbell denied it was him, claiming that he had not left his house.

However, footage from his own doorbell camera was also found. It showed him covering the lens with gaffer tape.

The footage was from February 16, 2024, the very day Mr Low is believed to have been shot.

His body lay undiscovered until the following morning.

Now, two years on, the trial moves into its final phase as the jury retires to consider its verdict. Much as they know in their hearts Campbell is the killer, neither the victim’s brother nor his partner are convinced justice will prevail.

Mr Low thinks it is 50/50. And, as deliberations continue into a second and then a third day, Ms Curran begins to fear the worst.

‘That was the longest three days of my life,’ she says. ‘You’re panicking inside. I’ve gone two years through hell waiting on this day to get Brian justice. Surely it’s obvious that he’s guilty.’

Not, it would seem, to the man in the dock. On hearing the word that seals his fate, he seems stunned and can be seen mouthing the word ‘What?!’

Brian’s brother Douglas Low wells up as Judge Scott recants parts of his victim Statement to Campbell

But it is the raw emotion on the face of Douglas Low that forms the most unforgettable sequence in the documentary as judge Lord Scott gives a flavour of the older brother’s victim impact statement.

His eyes fill with tears and his lips quiver as the judge tells Campbell: ‘He says his heart is broken with an overwhelming sense of loss and grief that words cannot express.

‘Brian was a best friend, a confidant, and almost like a son to him due to their ten-year age gap.’

As for Ms Curran, the judge informs the killer, ‘she feels sad every day and misses Brian. Her closest friend told her “the spark has gone out of your eyes. You just appear sad. It’s heartbreaking.’”

It is the reactions – even micro-reactions – of the key players in the trial that make this such compelling television. No one in the public benches and no reporter, however eagle-eyed, could pick up on everything those all-seeing lenses do.

Kate Reid, who directed the documentary, tells the Mail: ‘Open justice is a foundational principle of the UK legal system – anyone can walk into a courtroom and watch a trial.

‘The Scottish judiciary has extended this to include permitting cameras in court, in certain circumstances.

‘During the filming of this trial, we used small, remotely operated cameras in the courtroom, so that the experience of attending court is unchanged.’

She adds: ‘Filming a live murder trial is not straightforward – a huge number of elements need to fall perfectly into place for it to be possible. 

‘Our whole team is acutely aware of the privilege of being behind-the-scenes during a murder trial.’

Judge Scott laid bare the emotional impact of Campbell’s actions on the friends and family of Brian Low

The end result is more than a courtroom drama, however. It is a portrait of the lives destroyed by the appalling act of violence which preceded the trial and of their anguished wait to discover whether justice is delivered.

Ms Reid adds: ‘In the making of this documentary, we had the privilege of filming with Brian Low’s brother, niece and partner.

‘Their strength, dignity and commitment to justice for Brian, is plain for all to see. For them to trust us with telling this story, means everything.’

Leaving the dock, moments after being sentenced to a minimum jail term of 19 years, a grim-faced Campbell glances up at his family once more.

This time he blows no kisses.

Part one of Murder Trial: Death of a Dog Walker is on BBC Scotland on Tuesday at 9pm. Both episodes are available on BBC iPlayer from Tuesday.