A guy who does something like this is a natural risk taker.
If you believe he's gulity, elements of his behaviour post massacre are risky, in the sense of appearing gulity, selling off stuff, callously putting the dog down " cos it will knacker my stereo " selling pictures of Shelia to the sun, drinking benders, drug benders, all in view of the police.
After the crime if gulity he didn't try to cover his tracks, " he was like fuck it, it's time to party, he apparently even said" right that's it times up" after his dying swan funeral act.
And to tell a woman of what he's done when he's playing around on the side with other women , and he's planning to leave her confirms. Shows his " recklessness" but the car journey isn't " reckless"
There's no way he wouldn't drive through fear of being seen.