WARNING: DISTRESSING CONTENT Elliot Rodger butchered six people because he was a virgin and had been constantly rejected by women
When Elliot Rodger slaughtered six university students he had never met, the world united in grief.
But when it emerged that the 22-year-old had carried out the senseless murders of innocent victims because he was virgin who had been rejected by women, grief turned to horror.
Rodger's horrific actions exposed a chilling online underworld of the Incels, meaning involuntarily celibate.
Disturbing forums reveal dark and violent threads between men who have been rejected by the opposite sex.
But Rodger's violent murders were the first time this has spread from the internet and into the real world - it would not be the last time.
BBC Three documentary, Inside the Secret World Of Incels, has spent time with those part of the online sub culture.
Before embarking on his killing spree in May, 2014, Rodger had uploaded a chilling video to YouTube, detail exactly why he wanted to target women.
In it, he says: "I'm not allowed to enjoy life in this world because I have been cast out, no one likes me and no one accepts me.
"These beautiful blonde girls should be walking with me, not those brutes. I deserve them more.
"Girls aren't sexually attracted to me. There's a major problem with that and it's a problem I intend to rectify."
Rodger, who was angry he was still a virgin and wanted to be a "true alpha male" planned to bust into a sorority house and "slaughter every, singlem spoiled, blonde, stuck up a s***."
First, he stabbed three men to death in his apartment before driving to one of the sorority houses attached to the University of California in the quiet town of Isla Vista, Sanata Barbara.
Rodger was unable to get into the house and thwarted he began firing at random, killing three women on the street.
A male student was gunned down inside a deli before speeding around Isla Vista, randomly shooting and hurting several people out walking on the streets.
His murderous rampage finally ended when he crashed his car and when officers opened the door, they found him dead inside.
Rodger had shot himself in the head.
While Rodger's horrific actions horrified people around the world, it catapulted Incels into people's minds and he became a 'hero' in the underground community.
He is idolised by the sexually frustrated men who identify as Incels and has even been dubbed 'Saint Elliot'.
Katherine Cooper was one of Rodger's six victims. She was shot eight times, once in the side of her head.
Her parents are still coming to terms with her death but say they are thankful her "wrong place, wrong time" murder saved dozens of lives when Rodger couldn't gain entry to the sorority house.
Katherine's father, Dan, said: "We believe her death saved 50 or 60 lives and when you're in our positions, you look for any silver lining."
In eight months of unprecedented access to the Incel community, the documentary reveals the darkest side of the young men who identify with other versions and feel extreme sexual frustration.
Some of the Incel forums have as many as 40,000 members, many discussing the rape of women.
And while the majority of the discussions remain solely in the online sphere, several spill into the real world.
Rodger's actions are believed to have inspired at least three other mass killings in North America.
Alek Minassian, 25, left 10 people dead when he ploughing through pedestrians on a packed street in a rental van in Toronto, Canada.
Minassian apparently made shortly before the attack which praised British mass killer Elliot Rodger.
One Incel is known online as Catfish.
He openly admits to subjecting his ex girlfriend to domestic violence and was subjected to a restraining order after they broke up.
Catfish says he has been rejected by more than 100 women and now makes it his mission to "expose how females really are".
His bizarre method is to upload a fake dating app profile, using a picture of a male model, and arrange to meet any of the women he meets online.
Catfish himself then turns up to the date and when the women realise they have been duped into meeting someone entirely different and leave, he films their horrified reactions.
He screams abuse at them and in one disturbing encounter yells obscenities at the woman who believes she is meeting a very different man.
Chillingly, he also encourages the women he has tricked to send initimate images and videos and is idolised on the Incel forums for his actions.
Catfish says: "People calling me a hero is better than sex.
"I confront them and tell them they are a horrible person. If they saw me on the street, they would ignore me.
"I'm just exposing who they are as individuals. I respect people but when it comes to females, I don't care.
"Women aren't people and I'm spreading awareness of how these females are."
In County Down, Northern Ireland, one man is determined to shake off his Incel status.
After spending years isolated and alone, never having had sex, kissed or even hugged a woman or held her hand, he is working hard on his self-esteem.
Mental health battles and suicidal thoughts are common place but he has turned to YouTube and makes videos charting his battle to happiness.
He said: "I would close myself off from the world and just lie down.
"Last Valentine's Day I thought if I don't have a girlfriend I will kill myself."
Desperate to make himself more attractive to women, he turned to steroids in a bid to bulk up.
He has now stopped taking them but has been left covered in spots.
However, he has attracted the attention of a woman who has also never had sex or been kissed and the pair have been chatting online and have started a relationship.
He said: "You need someone to step in and show you the light because as Incels we can be lost in darkness."
This is a message Rodger's victim Katherine Cooper's parents also firmly believe in.
Rather than drowning anger, they want people who have the same feelings as their daughter's killer to be able to access the help they need.
Her dad, Dan Cooper, said: "Our daughter died because some individual couldn't cope.
"His parents missed it and anyone who was trying to help him missed it and my daughter paid the price.
"If we want to stop this happening again we need to get to the individual and reach them and help them and make them realise suicide isn't the way out.
"Going out with a bang to make the news isn't the way out.
"I hope those that idolise this individual will see what the action do to people and see how pointless this really is.
"If there had been people to help him through it, my daughter mght still be here.
"That person is gone, he doesn't feel a thing but we feel it every day and that's our reality now."
- Inside The Secret World Of Incels will be on BBC Three on Sunday, July 14.