at the end of season 3 and throughout season 4, dexter kept on saying he has now mastered harry's code, but I disagree. it seems to me he kept making mistakes due to lack of sleep and exhaustion.
ok, when dexter needled trinity for the first time and put him in the cargo van, why didn't he just drive off? why did he have a brain freeze and just gave up to the cops about the hit and run?
he could've easily waited an hour until the cops leave and then driven off with the van to do his ritual. I thought that was really dumb. when he stuck the needle in, I was like, "YES!" he got him. Only to let him get away. Also, he could've at least bound trinity's hands and feet and gagged him so that he couldn't escape from the van.
for a "master" of Harry's code, he really wasn't using his brain in that situation...
it feels like right after they shot that scene, someone said, hold it! it's too boring for Dexter to do his ritual now, let's create all this other crap that has a bunch of plotholes to keep it more exciting for the viewers. oh ya, let's kill rita off too!
I just thought he could've easily waited an hour and then go do his ritual on arthur....if not that, at the very least, bind and gag the mofo!