Mystery surrounds why a mother and her six-year-old twins were brutally murdered

Mystery continues to surround the brutal murder of a mother and her young twin daughters, with a new episode exploring it further.

The latest episode of Secrets of the Hells Angels will look into the shocking murder of a mother and her twin daughters.

The brutal murder of a mum and her two daughters

Margo Compton was killed on August 7, 1977, alongside her six-year-old twin daughters, Sylvia and Sandra.

In her addition to her girls being slaughtered, the 19-year-old son of Margo's boyfriend also lost his life.

Detective Sergeant Mike Graham has worked tirelessly to try and find the killer for years, and one detail that jumped out to him about the horrific crime was how one of the girls was clutching a toy from a Cracker Jack box when she was shot in the head.

In the new episode of Secrets of the Hells Angels, Detective Graham's 18-year journey for justice is laid out.

Speaking in the show, he said: "I had withheld a little bit of evidence from the public. And Michael [Thompson] knew it. That's when I knew that Michael was telling me the truth."

Margo Compton was killed alongside her daughters in 1977. (A+E Networks)

Who is Michael Thompson?

Thompson was the leader of the Aryan Brotherhood prison gang, who Graham met in 1984.

This gang ran methamphetamine sales inside California prisons, whilst the Hells Angels biker gang ran the market on the outside.

Often, the Hells Angels would join the Aryan Brotherhood when they were imprisoned.

When a meth supplier, Odis Garett, was put behind bars, he began talking to Thompson about the Oregon murders.

This information was then relayed by Thompson to Graham.

Thompson recalled that Graham was very direct and upfront.

He said: "[Graham said] ‘Look, I don't really care about you, but I have a passion and my passion is to come to terms with the execution of these two little girls and Margo Compton. And I said, 'Well, we share that'."

The twin girls' murders went unsolved for years. (A+E Networks)

As rumours spread in the prison that Garrett was the killer Thompson gave him the cold shoulder.

Eventually, Garrett admitted to him that he had ordered the killing of the girls.

And as for the man who had pulled the trigger?

It was Robert G. McClure, a Hells Angels 'hang-around' - not an official member of the group.

Thompson took this information to the authorities.

Why had the young mother and her children been targets of the gang?

Compton had testified against several Hells Angels members during a prostitution trial in San Francisco - ultimately making her a target for retaliation.

Garrett himself was landed with a conviction in the case for ordering McClure to have Compton and her family murdered.

At McClure's trial in 1994, the judge deemed the crime one of the 'most egregious' he'd ever come across, branding McClure 'heartless and cold-blooded'.

During the trial, one witness claimed that McClure had even bragged he'd forced Compton to watch as he murdered her daughters.

Secrets of the Hells Angels airs every Saturday on A&E.