It's the one where Galactor tries to assassinate Dr. Nambu, and one of them uses the same exploding roses that were used to kill Joe's parents. From this episode, I would have to say that Joe's parents were fairly important people to be targeted by Galactor, and that Galactor's been around for at least 20 years, such that it's members could have kids who could then be raised to fight for Galactor from birth. Whether any of this will be explored in the show, I can not say.