Changing at WHF doesn’t bring it back to his cottage, he doesn’t know if his cottage would be searched, traced etc at this stage, rather risky I would have thought?
What would be brought back to his cottage?
Possible a few drops of blood on his clothes. Which would have dried by the time he arrived back. These clothes were going straight into the washing machine.
It's possible his cleaning up took place both at WHF & his cottage.
Believe his main focus at WHF would be to carry out the massacre, stage the scene & get back to his cottage as soon as possible.
May have washed his hands at WHF. If there was blood on them at any time.