Patrick David Mackay was born on September 25, 1952, at Park Royal Hospital in London. He grew up in Dartford, Kent, with his parents and two younger sisters. His father, Harold Mackay, was a Scottish accountant. His mother, Marion Mackay, was of Creole descent from Guyana. Patrick had two sisters, born in 1954 and 1957.

As a child, Patrick faced physical abuse from his father. He struggled in school, often getting poor grades. He was known to bully his classmates and frequently threw tantrums. A classmate described him as "like a little terrorist," noting that he would physically attack other children. Patrick also displayed cruelty toward animals, such as tearing the wings off birds.

When Patrick was ten, his father died from a heart attack caused by alcoholism. Harold's last words were, "Remember to be good." Patrick had trouble coping with his father's death, claiming that Harold was still alive and keeping a photograph of him with him. Patrick did not attend his father's funeral, as his mother advised against it.

After his father's death, Patrick took on a 'father figure' role in the family. This led to more violence, as he began to beat his mother and sisters. The family later moved to Gravesend, but the situation did not improve. Police were often called to their home, sometimes as frequently as four times a week. Patrick’s temper became extreme, and he frequently directed his anger at his family members.

At 15, he was diagnosed as a psychopath by a psychiatrist named Dr. Leonard Carr. The doctor warned that Patrick would likely grow up to be a "cold, psychopathic killer." Between the ages of 12 and 22, he was removed from his home 18 times and placed in various specialist schools, institutions, and prisons. One teacher described him as "a potential murderer of women." In October 1968, he was committed to Moss Side Hospital in Liverpool as a diagnosed psychopath. He was released in 1972.

Patrick David Mackay engaged in a series of violent crimes in the 1970s. After his release from an institution in 1972, he began a crime spree in affluent London areas like Chelsea and Knightsbridge. These areas saw an increase in muggings and thefts, with elderly women often targeted. Mackay would befriend these women to gain access to their homes and then commit the crimes.

On February 14, 1974, Mackay murdered 84-year-old Isabella Griffith in her Chelsea home. He physically assaulted her, strangled her, and stabbed her. The police could not identify him at the time, and the petty crimes continued in the area. The following year, on March 10, 1975, he killed Adele Price. He entered her home under the pretense of asking for a glass of water, and as he left, her granddaughter unknowingly walked past him.

A few weeks later, on March 21, 1975, he brutally murdered Father Anthony Crean in Shorne, Kent, using an axe. Witnesses later confirmed seeing Mackay near Crean's home. This murder brought attention back to Mackay, as he had a previous connection to the priest, having once stolen from him.

After his arrest for Father Crean's murder, police discovered fingerprints linking him to the earlier murders of Isabella Griffith and Adele Price. They also found stolen items in his home that had been taken during robberies in Chelsea. Mackay led detectives to a location in Clapham, stating he discarded a knife used in the killings there.

While in custody, Mackay confessed to murdering Crean, Griffith, and Price; however, he later mentioned killing six more people. His descriptions matched several unsolved murders, including the death of Heidi Mnilk, a young au pair, in July 1973, and several others throughout 1974 and early 1975.

In November 1975, Mackay stood trial for the murders. He pleaded guilty to manslaughter based on diminished responsibility for the killings of Griffith, Price, and Crean. Evidence hinted at his involvement in other murders, but he was not convicted of those due to insufficient evidence. He received a life sentence with a minimum of 20 years in prison.

Over the following decades, Mackay was repeatedly considered for parole but was denied due to being deemed too dangerous for release. He spent many years in facilities for dangerous prisoners, with reports of his violent behavior persisting. In 2022, his case was reviewed again, raising concerns from victims' families and the public. As of 2023, he has remained in prison, serving time for his crimes.