Pine was the only other person on Quentin's car besides Yhitzak and Yhitzak has lived in a free system all his life. Also, when Pine separated from Mopook the Sneaky, he might have also ditched the ZAG.

Krakens kick major ass!

is my main suspect in being involved with the bombing and the ZG.  Oh, I don't think he's a fallen member of the ZG but one of the leaders on Ionath. After all, he is not searched when he comes home from other areas of the galaxy so instead of smuggling drugs he's smuggling explosives.  If I remember correctly, they only inspect the ship itself for explosives.  Also, I supsect he's the one who snitched on Don Pine to Gredok and what Quentin did to help him.  I think he views Q as a "race traitor", especially after he refused to give him the ball, and may have been trying to kill him at the parade.  More than likely it was just to spread mayhem and terror rather than having a specific target.
 What kills us, doesn't make us stronger.

Not him personally but his family. We know very little about them and the bats asked him what his connection was, there has to be something there, he just doesn't know about it. At some point someone that cares a lot about him has been involved and then left. Revenge hit on Q instead of them as that'd be much more devestating. It would also explain why his parents haven't tried to contact him (assuming they are still alive). They have to know who he is it's such an unusual name and it's all over the Galaxy
-- Death, chaos and mayhem, the music of the night

Q's family never crossed my mind, but it would make sense.  That's a good theory too, I like it.

My own personal theory, I think its Yassoud.  Let's face it, we really don't know that much about him.  We can't say for sure the bomber got the right car, they could have been trying for another car and jumped the gun, we just don't know.  And Yassoud pretty much falls apart after the bombing.  Starts playing badly, drinking way more than usual, doesn't give a crap about games or anything else, starts keeping to himself more.  That is a totally different person than we saw in The Rookie, and we can't blame it all on his playing badly because he wasn't playing too great in The Rookie either.

Do not mess with the affairs of monsters, for you are tasty and good with ketchup.

Quinton and I think they where trying to get at his family.