For the sheer terror of it - the worst thing you can do to people is aim at their children.

Lee Boyd Malvo
May 23, 2006
Rockville, MD trial of John Allen Muhammad
In response to being asked why Muhammad devised a two-phase plan to shoot as many as six random people each day for 30 days in the Washington area and then target children and police officers with explosives.  They planned to place explosives on school buses in Baltimore, kill a Baltimore police officer and then set off explosives packed with ball bearings at the officer's funeral.  Malvo also testified Muhammad hated America, introduced him to the teaching of the Nation of Islam, and thought white people were "the devil".
[Islamic extremist.  Racist.  Murderer.  Conspiring to murder children.  The death penalty is clearly appropriate for Muhammad.--Joe]

Update: Far more details are in the Washington Post article.