BBC true crime doc reveals how horrific murder was solved after 35 years thanks to cigarette butt

A new BBC documentary will look into a horrific murder that remained unsolved for 35 years until an unlikely piece of evidence helped catch the killer.

Mary McLaughlin died on 26 September 1984 and was found strangled to death in her own bed six days later.

Eventually, her murder was solved due to advancements in DNA technology and a cigarette butt left at the scene of the crime.

Her killer Graham McGill would be back behind bars the next day, but wouldn’t face justice for her death until 2021, following a DNA discovery in 2014.

She was killed at 58 (BBC)

McGill was a serial sexual offender who was out on a scheme called ‘Training for Freedom’, away for a period from his prison more than 50 miles away.

He was on the last day of his approved leave, and was due back behind bars the next day, police none the wiser. Less than a month after her killing, McGill walked free from prison.

The case will be explored in BBC's Murder Case: The Hunt for Mary McLaughlin’s Killer which first aired this year on BBC Scotland and will air tonight at 9.00pm.

Mary’s body was found by her son face down on a bare mattress, having been strangled to death with a dressing gown cord.

She was 58 at the time of her death, a mother of eleven, and police were unable to find a suspect.

McGill killed her after following her home (Police Scotland)

McLaughlin was out at the pub on the day of her murder, with McGill reportedly having followed her home.

The pair struck up a conversation and he offered to walk her home, with prosecutor Alex Prentice saying: “Mary McLaughlin was someone who was friendly and trusting and I would suggest that ultimately brought about her death."

It is believed the ‘violent’ assault carried out by McGill was sexually motivated.

Despite more than 1,000 statements being taken, police had no idea who had done it until, in 2014, a new DNA testing facility was opened.

Investigating officers reopened the case, with particular focus put on a cigarette found at the scene.

It stuck out due to the fact that it was not the brand she would usually smoke, and was sent off for testing.

A cigarette left at the scene of the crime ended up solving the case by linking DNA evidence to the killer (BBC)

The butt was found to be a direct match and, although investigators were perplexed as he was in prison at the time of the killing, they realised he had been out that night.

He was ultimately charged and, in 2021, sentenced to a minimum of 14 years in prison after a trial in which he denied killing her.

The judge said of the case when passing his judgement: “She was 58 when she died and you were 22. You are now 59.

“Her family has had to wait all that time in order to discover who was responsible for that act knowing that whoever did it was probably at large in the community.

‘’They had never given up the hope that someday they would find out what had happened to her.

“They have been deprived of her love and companionship.

“It is due to the perseverance of police authorities, and in particular the forensic biologists, that your guilt could be demonstrated.”

Murder Case: The Hunt for Mary McLaughlin’s Killer will air on BBC 2 tonight, February 19, at 9pm.