это еще не все?

Nineteen "black widow" female suicide bombers trained by an Islamist terrorist known as "the Russian Bin Laden" remain at large and may launch fresh attacks on Moscow, Russian investigators have warned.
The warning will heighten fears that Monday's rush-hour suicide attack on the Moscow metro by two women may just be the start of a large-scale terror campaign.

Investigators have said they were trying to confirm whether the two women were part of what was originally a 30-strong female "martyrs' brigade".The terrorist who trained the brigade, an Islamist convert calling himself Said Buryatsky, was killed in a special forces operation earlier this month in Ingushetia.
Investigators said the late terrorist, whose real name was Alexander Tikhomirov, had recruited 30 potential female suicide bombers in Chechnya and Ingushetia and dispatched them to Turkey to be taught the precepts of radical Islam in an unnamed Madrasah.
On their return to Russia, he had personally continued their "education." The women are known as "black widows" because they have usually lost husbands or close relatives in clashes with Russian forces and are motivated by a desire for revenge.

Nine of the original thirty brigade members are known to have already blown themselves up in the lawless North Caucasus region along Russia's southern flank where suicide attacks started up again last year after a long pause, and two more are thought to have blown themselves up in the Moscow metro on Monday.

But that, say investigators, leaves 19 "black widows" at large.
No group have claimed responsibility for the bombing.
http://www.telegraph.co.uk/news/worldnews/europe/russia/7538556/Moscow-metro-19-black-widows-could-launch-fresh-attacks.html

Почему они не берут на себя ответственность за взрывы?