In February 2004, the FBI announced it would review its investigation after learning that agents in the investigation of the Midwest Bank Robbers (an alleged Aryan-oriented gang) had turned up explosive caps of the same type that were used to trigger the Oklahoma City bomb. Agents expressed surprise that bombing investigators had not been provided information from the Midwest Bank Robbers investigation. McVeigh was given a one-week delay prior to his execution while evidence relating to the Bank Robbers’ gang was presented to a court.

White Supremacist involvement was believed to be associated becasue of the circumstantial evidence above but I’ve never heard of suspected republican guard involvement.