Interesting theory. But there are several holes in that one.
The diplomat that Tony was supposed to help have killed was an enemy of those in the Drug trade. And his own people knew it. So it is not unlikely that they would randomly check his house, office or car for bombs, etc. I think that they legitimately found that bomb.
I think that Sosa was on the up and up at first with Tony. Remember that Sosa and his associates were making a whole lot of money dealing with Tony, and $$$ are what the bottom line to these people is all about. Besides, why wouldn't Sosa want that guy dead? That guy was going to have Sosa and his buddies put away for a very long time by making his speech.
Good question though. And please keep em coming.
I highly suggest that you read RETURN OF SF.
http://www.thereturnofsf.com/store.htm Don Cardi