Who is Andrew Cunanan? Why did he kill Gianni Versace?

• The Assassination of Gianni Versace is an "inaccurate portrayal" of events, says his former lover
• Versace family labels "unauthorised" American Crime Story starring Penelope Cruz as a "work of fiction"

Cunanan never stood trial – his body was found on a Miami houseboat nine days after the Versace murder; an apparent suicide – and as a result, much of the public knowledge about him comes from Orth's book, which remains a subject of controversy: the Versace family have said recently that the book is full of "gossip and speculation", while Cunanan's own family have refused to accept its findings as true.

Here is everything we know about the elusive figure.

Who is Andrew Cunanan?

In the days following Gianni Versace's death, Andrew Cunanan, a 27-year-old, half Filipino/half Italian socialite became the subject of one of the biggest manhunts in US history. He was already on the FBI's most wanted list as the prime suspect for the murders of his friend Jeffrey Trail, ex-lover David Madson, 72-year-old Chicagoan real estate developer Lee Miglin and cemetery caretaker William Reese, but the Versace murder accelerated the chase significantly.

While there has been much speculation as to the motive behind the murders – Orth's book posits the theory that Versace and Cunanan were connected to the mob, though there is little evidence to back this up – the police were never able to pin anything down. In an attempt to make sense of the story, Vanity Fair journalist Orth – who had begun to investigate Cunanan before the Versace killing – conducted over 400 interviews with individuals close to the case, from law enforcement officials to family members, friends and acquaintances of the alleged murder, from his youth in La Jolla, San Diego, right up to his spell as an alleged crystal meth dealer and user in the city's vibrant gay scene.

Why did Andrew Cunanan kill Gianni Versace?

In truth, we will probably never know. The best theories are based upon speculation, albeit somewhat logical speculation. Testimonies from Cunanan's friends paint him as a textbook narcissist; a pathological liar. The Greek chorus assembled by Orth deems him a deeply materialistic man obsessed with wealth and social status whose drug-fuelled downward spiral sent him on a psychotic five-person killing spree.

While the police originally explored the possibility that Cunanan had become violent after he discovered that he had contracted the AIDS virus from Versace, the autopsy revealed that he did not have the disease. It was never proved, either, that Gianni Versace had the virus, though Maureen Orth suggests that he did in Vulgar Favours, and it is also suggested in TAOGV (Penelope Cruz's Donatella Versace mentions that her brother is "sick").

According to a unnamed drug dealer cited by Orth, Cunanan began to use crystal meth regularly in 1993, and soon thereafter started dealing drugs to fund his lavish lifestyle. This, it is suggested, might have been the beginning of a downward spiral that culminated in a financial bottom-out after a breakup, in mid 1996, with San Diego businessman Norman Blachford who had given him an allowance of $2,500 per month.

Whether or not his drug use was a factor, there is little doubt that Cunanan's mental state was in steady decline in the months leading up to the murders. He left San Diego over $40,000 in debt, and one of his last encounters with a friend from university, John Semerau, ended rather ominously.

"He grabbed me around the neck so hard he was choking me by his grip," Semerau told Orth. "He kind of spiralled. Over the last six months, whenever I ran into him, he was particularly aggressive."

"Andrew was hunting, getting the thrill of the hunt, the thrill of the kill," he went on to suggest. "I saw it in his eyes. I saw it in his body. He had stepped over the edge."

Soon afterwards, Cunanan arrived in Minnesota where his killing spree began.

The Assassination of Gianni Versace airs Wednesdays at 9pm on BBC2