On the wall of James Holmes' prison cell is a small blue square panel pinned with selfies and photographs of attractive young women who have all contacted the man who shot dead 12 people inside a packed Colorado cinema.

The disturbing and confusing collage is made up of around two dozen blondes and brunettes, some smiling, others smouldering; several pose seductively in various states of undress.

It might be the Instagram feed of a young single man, except it's not.

These women have all sent letters with their photographs to the 27-year-old cold-blooded killer who slaughtered 12 people on July 20, 2012, during a screening of The Dark Knight Rises .

James Holmes did not receive the death penalty for murdering 12 people in a Colorado movie theater.

This unsettling and perplexing case of Holmes' fandom was revealed after Colorado’s District Attorney Office released photos from the inside the killer's cell.

And the pretty faces on the blue pin board are just the tip of the iceberg, Rich Orman, senior deputy district attorney, told NY Daily News .

"Those are young ladies who sent him their photograph," Orman said.

"They sent him tons and tons of letters, and he hung up some of their pictures."

In the centre of the photograph collage is an odd hand-drawn sketch of an infinity sign and the number 1.

Colorado police found the exact same drawing on a calendar in Holmes' apartment. He had drawn it on July 20, the day of the movie massacre.

Serial killers and some of the worst criminal offenders are regularly sent fan mail and love letters. Even prisoners on death row, paying the ultimate price for the most heinous of crimes, will get married to 'prison brides'.

Psychologists are uncertain over the reasons for the phenomenon.

However, hybristophilia is a known paraphilia in which a person is sexually aroused by being with a partner who has committed crimes and atrocities.

In one of the more bizarre prison bride episodes, Afton Elaine Burton, 27, got engaged to notorious murderer Charles Manson.

But the romance failed when Manson learned his young admirer was seeking his hand in marriage so that she would gain the right to his corpse when he died.

It was reported Ms Burton's cunning money-making plan involved putting Manson's corpse on display in a glass cabinet, like Lenin.

Aurora cinema shooter James Holmes was last month sentenced to life in prison without parole.