Vreenak

[Paradise City]

Garak said he was going to sneak inside the Romulan shuttle looking for intelligence information so that's the ample opportunity right there to plant the bomb.

Interesting. What stage of the episode was this? If he did use this little clandestine visit as an opportunity to plant the bomb then it's highly likely from this point on he had decided to kill the Senator come what may. Otherwise Garak's bomb would've been left there unused if the rod had passed inspection.

 

[Finn]

^Not long before we see the senator arrive. And not necessarily. Garak probably wanted the bomb to go off even if Vreenak decided the rod was fine.