Russian authorities took little time saying that female suicide bombers from the Northern Caucasus are suspected of carrying out the morning attacks that killed at least 36 people and injured dozens more in Moscow. This BBC backgrounder explains why there are so many Chechen women willing to kill themselves to inflict terror. Russian soldiers fighting in Chechnya have left countless women widowed, or killed their sons, brothers or fathers. They have also raped many who afterward find it hard to live a normal life. Post-traumatic stress disorder is reportedly widespread among Chechen women. And Chechen rebel leader Doku Umarov is thought likely to use female suicide bombers.