David said Robin was wearing the clothes (tracksuit) he had been wearing the previous night.

Robin wore a little woollen beanie at night to keep his balding head warm. If you are to believe the Bain Defence scenario, he would have also had that on while fighting Stephen and yet somehow it remained on his head, blood-splatter free and wasn’t pulled off in the struggle or lost in the chaos.  It was still on him when he was found.