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This is the three-part trailer for a docuseries looking back at one of the most tragic murder cases in the area.

Crime + Investigation channel will recount the heart-breaking and horrific story of Anne Cook, an identical twin who was stabbed to death while walking her dog in Munden Park, near the A41, in 2000.

She was stabbed in the heart with a kitchen knife by complete stranger, Leon Paul Amos, from Watford, who was convicted in 2001 and sentenced to life in prison.

This episode of Murdertown, hosted by Happy Valley, Corrie and Mr Selfridge actress, Katherine Kelly, will air on national television on October 15 at 9pm.

Each episode focuses on one murder in one UK city.

Miss Cook, an internet designer, was walking her King Charles Spaniel, Elvy, when she was attacked by Amos.

She is survived by her twin sister Susan Cutler.

Amos, who was 35 at the time, had stalked another woman earlier that day, had a previous conviction for rape and had also held a woman at knife-point with the intention of raping either her or her daughter.

The court heard that Miss Cook, who carried a small lock knife, was stabbed through the heart by Amos in Watford, on May 9, 2000. She had been given the knife by her brother-in-law because she had become increasingly terrified of being attacked.

Amos then took her knife and her mobile phone.

Although she bravely tried to fight him off, he plunged a knife into her heart and then fled the scene.

Amos, who denied murder, took Miss Cook's mobile phone before running through bushes, scaling a 6ft fence topped with razor wire and crossing six lanes of the M1, forcing cars to swerve to avoid him.

He was arrested nine days later.

After he was convicted, Susan said of her sister: “She was a hard-working, honest and lovely person. She wasn't my best friend, she was my second self."

The Watford edition of Murdertown will air on national television on October 15 at 9pm.