Since he was observed wearing gloves in public in PA, how do you know he wasn't wearing regular men's cold weather gloves to class in WA?
Pretty easy to cover up bruises and scratches, btw. I do it all the time, as I have a wild puppy and get some tremendous scratches which I prefer not to show to my students. I simply use a small amount of foundation. But if it were just sitting as a student in a class, I'd of course wear a long sleeve shirt and gloves if I had a scratch on the back of my hand (which is not at all the most likely place for this defendant to have been scratched in the first place.
I believe that since he apparently left a full enough DNA profile for LE to hit up GEDMatch, that he very likely cut himself (above article I linked from NYPost and an interview that may or may not be allowed here call him "clumsy"). Since I believe he wore anti-cut gloves, a mask and long sleeved jacket, and I believe he used a particular set of techniques to accomplish his crime swiftly, I think the most likely place that he would have cut himself might well be a leg (he likely used his body weight to pin his victims down while he attacked them, primarily by pressure from his knees, leaving his upper leg vulnerable).
This is just my speculation about the nature of possible cuts (perhaps quite superficial). We await the actual information either at the opening of the PCA or at trial.