WASHINGTON (CNN) -- Former New York City Mayor Rudy Giuliani commemorated the 12th anniversary of the Oklahoma City bombing Thursday, comparing that tragedy to the Virginia Tech shootings earlier in the week.

"This week it is hard not to note that America was again shaken by horrible, horrendous violence, again on an early morning in April," The GOP presidential candidate said. "All Americans' thoughts and prayers I know, are with the families of Virginia Tech, and with the wounded students who are still fighting to recover."

Giuliani, who often touts his leadership during the events of September 11, also called for continued "offense" against terrorists.

"We need to show the ultimate defiance to terrorists," he said. "The way you defeat terrorists is not only to be vigilant, to be on offense that we have to be, but also to determine to live our lives with freedom from fear."