Who is H.C. Wickel? The FBI wants to know.

The name was on a typed return address label on the mail-bomb package that killed an advertising executive Saturday. Authorities hope it's a clue that helps unravel the mystery of the Unabomber, who has killed two people and injured 22 in 15 bombings since 1978.The label said Wickel was from the Department of Economics at San Francisco State University. But no such person has ever taught or enrolled at the school, said Jim Freeman, head of the San Francisco FBI and leader of the Unabom Task Force.

"The task force has been investigating extensively all leads that relate to the identity of this return addressee, and that has been without success," Freeman said Wednesday.