Excellent clarification.
I'd add only that a dry suit keeps water out by using durable seals for arms, legs and neck. The suit material proper is thick, scrunchy and repels water (and would repel blood, etc). You're looking at $$$ for one and it makes a good bit of noise while moving. You're not sneaking up on much in a drysuit -- maybe victims who are sleeping heavy. Maybe.
A wetsuit will absorb any liquid it's confronted with to some degree, whether immersed in it or not. It would offer some insulation from sharps and is less noisy, if far warmer than a drysuit. You're not going to peel if off to reveal a tuxedo that's anything but damp, stained and rumpled.
It's possible of course that we have an aquatic-minded killer here. But if I were planning to do a deed most foul I would not take along my cherished drysuit or even full soaker. I'd spend anywhere from 1200.00 to 700.00 less and grab a bog-standard coverup suit, gloves and booties. Cheaper, lighter, can be bought for cash in a whole bunch of places and then removed, reversed, rolled up and discarded in any handy rubbish bin.
If this was planned, which seems likely, then my bet's on a perp prioritizing ease of use and disposal and lack of traceability over the ability to go for a swim after in comfort. The mooted method of ingress, weapon used and exit without being seen point to either luck and/ or some level of careful preparation for these attacks, possibly involving knowledge of the layout, escape routes and runthroughs, and a plan for getting rid of evidence.
My ha'penny's worth, for what it's worth.