Ukrainian serial killers Viktor Sayenko and Igor Suprunyuk - collectively referred to as the Dnepropetrovsk maniacs - brutally murdered 21 victims in less than a month and recorded their crimes in grisly videos, yet many are unaware of their horrific deeds.
In February 2009, Viktor and Igor were sentenced to life imprisonment. Viktor was found guilty of 21 murders; Igor of 18.
The killers, who met at school, smashed their victims' heads with metal rods, in some cases brutalising their bodies to such an extent that it was difficult to identify them.
As reported by local media, at the time of the pair's arrest in 2007 the then Ukrainian Deputy Minister for Internal Affairs Mykola Kupyansk said: "It is rather difficult to say about the motives. The murders were more like fun or hunting."
He added: "In some cases, they videotaped what they were doing."
Most notably, the pair were behind infamous viral snuff video '3 Guys, One Hammer'.
Their month-long grisly killing spree reportedly came about as a twisted attempt to deal with their respective phobias.
Igor tried to deal with a severe fear of heights by hanging off the railings of a 14th floor apartment for hours and looking down.
Meanwhile, the pair's friend and accomplice in two robberies (but not the murders) Alexander Ganzha had a phobia of blood, which Viktor suggested treating by torturing animals.
The pair claimed their first human victim in June 2007, attacking 33-year-old Ekaterina Ilchenko from behind with hammers. An hour after the first killing they also attacked Roman Tatarevich, smashing his head open after they found him sleeping on a bench.
Bodies continued to pile up rapidly until the pair attacked two 14-year-old boys and one of them, Vadim Lyakhov, managed to escape.
Although police initially suspected Vadim of murdering his friend, he was able to give a description of the real killers.
A few days later, another of Viktor and Igor's murders was witnessed by locals, who gave a description matching Vadim's.
Viktor and Igor were eventually arrested on 23 July after they were caught trying to sell a phone they'd stolen from one of their murder victims in a pawn shop.
Following a 2009 court case, the pair were sentenced to life imprisonment.