What have they in Common?

Below are pictures of innocent looking people.
What do you think they have in Common?

Top from left to right: Harold Shipman, Alexander Pichushkin and Gary Ridgway
Bottom from left to right: Dylan Klebold, Eric Harris and Seung-Hui Cho

They are all murderers. They kill a lot of people brutally.

Harold Frederick "Fred" Shipman (14 January 1946 – 13 January 2004) was a British convicted serial killer and former doctor. He is one of the most prolific known serial killers in history with 218 murders being positively ascribed to him, although the real number may be twice that.

Aleksandr "Sasha" Yuryevich Pichushkin (Russian: Алекса́ндр Ю́рьевич Пичу́шкин, born 9 April 1974 in Mytishchi, Moscow Oblast), also known as The Chessboard Killer and The Bitsa Park Maniac, is a Russian serial killer. He is believed to have killed at least 48 people and up to 61–63 people in southwest Moscow's Bitsa Park, where several of the victims' bodies were found.

Gary Leon Ridgway (born February 18, 1949), known as the "Green River Killer", is an American serial killer. Ridgway murdered numerous women in Washington during the 1980s and 1990s. He strangled them, mostly with his arm, but he would also use ligatures. After strangling the women, he would dump their bodies throughout King County.

Eric David Harris (April 9, 1981 – April 20, 1999) and Dylan Bennet Klebold (September 11, 1981 – April 20, 1999) were the high school seniors who committed the Columbine High School massacre. They killed 13 people and injured 21 others. Three people were also injured as they escaped the attack. Both Harris, 18 years old, and Klebold, 17, committed suicide at the site of the killings.

Seung-hui Cho (January 18, 1984 – April 16, 2007) was a senior-level undergraduate student at Virginia Polytechnic Institute and State University who killed 32 people and wounded 25 others in the shooting rampage which has come to be known as the "Virginia Tech massacre". Cho later committed suicide after law enforcement officers breached the doors of the building where the majority of the shooting had taken place.

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