Case strategy is always the lawyer's call. And while outsiders may think that they see something useful and not understand why the lawyer isn't paying much attention to it, there's usually a reason. You don't know all of the information the lawyer knows about the case, nor do you have any idea what long-term strategies he's got in his mind that he's hoping to be able to use.
Doesn't sound to me like there was a whole lot of time for him to have ditched that truck between his girlfriend's phone call and the arrival of the police, though depending upon where the drugs were found, if the case goes to trial
, he can then possibly bring out how many others had access to the truck and could have left the cocaine in it. Also, a blood test would not negate the possession. It would only mean he hadn't recently used.
Your son's case might have a search and seizure issue, as even if the dog smelled out the cocaine, if the stuff was not in plain view, the officer should have gotten a warrant unless he believed he had a clear exception to the warrant requirement. To that effect, his lawyer is correct. There is a search issue here which needs to be inspected at a pre-trial suppression hearing down the road if this case is going to trial. The underlying domestic issue is potentially useful for trial too. If the ex-girlfriend called the police and your son waited for them to show up, perhaps it was the girlfriend who was able to plant the cocaine and set him up with the police. I don't see anything wrong at all with a strategy that would introduce that possibility to a jury. If you're correct that others could have planted drugs, why not her? She'd appear to have the best motive to want to frame him. It doesn't have to be true. It only has to be a possibility to create reasonable doubt in the minds of a jury.
Again, I'm just working on some very sketchy information that you provided me with. I don't know that if I were privy to all of the evidence his lawyer has that I'd be thinking in those directions. But based on the little I know, it would seem to me that your son's lawyer would appear to be on the right track. Remeber that it's the lawyer's job to get the jury to doubt the state's version of the case, because doubt equals an acquittal. Generally the lawyer will try to lay the grounds to show bring out as much doubt in the minds of the jury as the facts allow.
I think this may be what you wanted to know, but your actual question was not very specific. If you need to follow up, just use the reply link below and I'll be happy to add to my answer.