11-year-old serial killer's chilling confessional notes were dismissed as a 'prank' by police

An 11-year-old serial killer made a chilling confession in handwritten notes after brutally killing two other children.

Mary Bell was just 10-years-old when she murdered four-year-old Martin Brown.

She strangled the young boy to death and left his body in an upstairs bedroom of a derelict house in Newcastle, UK, where they lived.

Just weeks later after she had turned 11, Mary struck again and this time killed three-year-old Brian Howe.

Mary Bell first killed someone when she was 10. (Keystone/Hulton Archive/Getty Images)

Brian was last seen playing with Bell, her neighbor and accomplice Norman Bell, 13, one of his siblings and their family dog, but alarm bells were rung after the three-year-old failed to return home later that fateful afternoon in July 1968.

Later that night, Brian's body was found between to large concrete blocks which his killer - later revealed to be Mary - did in a bid to hide his body.

Brain also died from strangulation. But, unlike with Martin, Mary is said to have mutilated the boy's body with scissors, scratching his thighs and butchering his penis.

Before Brian's tragic death, Mary had penned notes admitting to her previous crime.

Such notes were discovered by nursery workers, with Mary and Norma having broken into and vandalized the establishment the night before.

The site in Newcastle where Brian Howe was found. (Mirrorpix via Getty Images)

As well as a defaced nursery, chilling notes were found. One read: "WE did murder martain brown f**kof you bastard."

A second even more sinister one penned by Mary said: "I murder SO That I may come back."

These notes were handed into the police, but they dismissed the notes as some kind of morbid prank.

After being questioned by police on several occasions, eventually Mary and Norma were found to have been involved with Brian and Martin's deaths.

They turned on each other during the investigation, with Mary trying to implicate Norma and Norma trying to place blame on Mary.

Toddler Brian Howe pictured with his mother before his murder. (MSI/Mirrorpix/Mirrorpix via Getty Images)

Both girls ended up being charged with manslaughter, but only Mary was indicted at trial.

A prosecutor said that the then 11-year-old murdered 'solely for the pleasure and excitement of killing', BBC reported at the time.

Mary was also described as being a 'very grave risk to other children if she is not closely watched'.

The murderous young girl went on to serve almost 12 years behind bars before being let out early on license.

She was released in 1980 when she was 23-years-old and given anonymity.

To this day, it remains unknown where Mary now lives and what name she's living under.