The headline exagerates a little. The “top official” is head of the criminal division for the US Attorney in Arizona.
(Committee Chairman) Issa released the following statement:
“The assertion of the fifth amendment by a senior Justice official is a significant indictment of the Department’s integrity in Operation Fast and Furious. The former head of the ATF has previously told the committee that the Justice Department is managing its response to Operation Fast and Furious in a manner designed to protect its political appointees."