THE unassuming postal worker stepped through the door of his apartment in Yonkers, New York, to find several police officers waiting for him. When they slapped handcuffs on the him and placed him under arrest he turned to one of the officers and said, “I guess this is the end of the trail”.

The date was August 10, 1977, 40 years ago today, and when the 24-year-old David Berkowitz was hauled into the NYPD headquarters in Manhattan, police were already breaking out the celebratory beers. The mayor had given a special amnesty on the usual ban on alcohol in police headquarters.

The reason for the celebration? Police had finally arrested the serial killer who had terrorised women since July 1976, taking six lives and wounding eight others. He became known as the “Son of Sam”, a phrase he used in a letter left near his victims.

Berkowitz pleaded guilty but would later tell police that Sam was a neighbour’s name and that “Son of Sam” was the neighbour’s black labrador, a demon who told him to murder women.

media_camera "Son of Sam" killer David Berkowitz, centre, is taken into police headquarters in New York City on August 11, 1977. Picture: AP

Berkowitz was the son of Betty Broder, whose first husband, an Italian-American named Tony Falco, had left her in 1940. In 1950 she began an affair with Joe Kleinman, to whom she became pregnant in late 1952. She refused to abort the baby and gave birth to a son she named Richard David Falco in June 1953. A few days later she gave him up for adoption to Pearl and Nathan Berkowitz.

At school he was a poor student, teased for being Jewish, he turned to bullying, theft and arson. After finding out that he was adopted he dreamt of finding his real family. He was close to his adoptive mother Pearl, but she died of cancer in 1967. Nathan married again, but Berkowitz didn’t like his stepmother. He left home to join the army in 1971, hoping to go to Vietnam, become a national hero and win a medal. Instead he served his time in South Korea, distinguishing himself for marksmanship.

Honourably discharged in 1974 he sought out his biological mother, but their relationship lapsed after he discovered the truth of his birth. He worked in a series of jobs, before finding work with the post office.

media_camera Serial killer David Berkowitz, known as "Son of Sam", at Attica Prison, New York, in 1979.

A loner who found it hard to relate to others, he roamed the streets at night prowling for women. In 1975 he attacked two women with a knife, hospitalising one — teenager Michelle Forman. He got away with it, but decided in future to use a gun.

He relocated to Yonkers, outside New York City and, in July 1976, approached two women sitting in a car in the Bronx. He fired at them with a .44 pistol, killing Donna Lauria and injuring her friend Jody Valenti, before quickly walking away.

In October he fired at the car of Carl Denaro, who was sitting with his girlfriend Rosemary Keenan. Although Denaro was injured, both escaped. In November, two women sitting on a porch in Queens — Donna DeMasi and Joanne Lomino — were shot but not killed. Then in January 1977, he shot dead Christine Freund and injured her boyfriend as they sat in a car. In March he shot and killed student Virginia Voskerichian as she walked home from Columbia University.

media_camera Three of Berkowitz’s victims (from left) Christine Freund, Virginia Voskerichian and Stacy Moskowitz.

Two more women sitting on a porch were shot but not killed in November in Queens. But in January 1977, he shot dead Christine Freund and injured her boyfriend as they sat in a car.

Police linked the crimes by ballistic evidence but were baffled by the random nature of the crimes. They noticed most victims were women with long, dark, wavy hair, speculating that he targeted Denaro because he had long dark hair and may have been mistaken for a woman.

Women began dying their hair blonde and cutting it short. People wondered where the “. 44 killer” would strike next. In April 1977 he shot and killed Alexander Esau and Valentina Suriani in their car in the Bronx, close to where he had killed Lauria. Near the scene of the crime he left a rambling letter telling police “I am the Son of Sam.” In May he sent another letter to a journalist signed Son of Sam. The name stuck.

media_camera Convicted murderer David Berkowitz responds during an interview in 2009. Picture: AP

Another couple were shot in their car in Queens in June, but survived. Berkowitz evaded police in the Bronx and Queens, and shot his final victims, Stacy Moskowitz and Robert Violante, in their car in Brooklyn. Moskowitz later died from her injuries.

Police tracked Berkowitz down thanks to a parking ticket he had received at 2.30am in Brooklyn on the night of the final murder. They wondered what a person from Yonkers was doing so far from home at that hour. Staking out his home, they arrested him when he emerged.

He spun his story about a 3000-year-old demon possessing a neighbour’s dog telling him to kill, but later admitted it was a lie in case he needed to plead insanity. He pleaded guilty and was sentenced to 25 years to life for each murder. He remains in prison.