Criminologist James Alan Fox says the uncle’s intuition is justified. In cases like this, he says, it is highly unusual for the younger participant — in this case, a sibling — to be the leader.

“I would be surprised,” says Fox, a professor of Criminology, Law and Public Policy at Boston’s Northeastern University. “Very surprised.”

Whatever their fraternal pecking order, when the bullets began flying in Watertown on Thursday night and 26-year-old Tamerlan went down, his younger brother ran him over — dragging him for about 30 feet — before ditching the car and fleeing on foot. After a 24-hour manhunt that shut down most of the Boston metropolitan area, police cornered the gravely wounded Dzhokhar hiding in a boat in a backyard, only blocks from where his brother bled out.