The most vicious of terrorist leaders are those who eschew violent acts themselves - there could be danger involved - but brainwash others into carrying out attacks. They should be pursued as vigorously and punished as severely as the pawns they train.
It now appears Tamerlan Tsarnaev, killed after he and his brother, now in custody, planted two bombs at the Boston Marathon, may have been under the influence of such an evil manipulator.
Family members say a man they knew only as Misha befriended Tsarnaev and converted him to a type of Islam that may have prompted him to explode the bombs.
Misha lives in the Boston area.
Investigators are being tight-lipped about the situation. It is not known whether they have found or talked to Misha.
Obviously, that should be one of their top priorities - as should contacting others who may have been influenced by Misha. If he proves to be a terrorist instigator he, too, should be arrested.