David Mulcahy was born in 1959 in the United Kingdom. He met John Duffy at Haverstock School in North London, where they formed a close and intense friendship. Both were known to have been victims of bullying during their school years. Mulcahy later married and had children, leading what appeared to be a normal life.

Between 1982 and 1986, David Mulcahy, alongside John Duffy, committed a series of rapes and murders near railway stations in Southern England. Their first known murder was of 19-year-old Alison Day on December 29, 1985. She was abducted near Hackney Wick station, raped, and strangled. Her body was found weighted down in the River Lea.

On April 17, 1986, they murdered 15-year-old Maartje Tamboezer in West Horsley, Surrey. She was knocked off her bicycle, raped, and then killed. Her body was set on fire in an attempt to destroy evidence.

Their final known victim was 29-year-old Anne Lock, who was abducted on May 18, 1986, near Brookmans Park station. She was raped and murdered, and her body was discovered weeks later.

Mulcahy was arrested on February 6, 1999, after Duffy implicated him in the crimes. DNA evidence and Duffy's testimony linked him to the murders and rapes. In February 2001, Mulcahy was convicted of three murders and seven rapes, receiving multiple life sentences.