It doesn't look like a professional hit, but perhaps an attempted robbery or drug deal that went bad, perhaps they walked in on the robbers
What evidence we have points to Mexicans doing it, and perhaps with the cooperation of a hotel staff employee. No professional killer would leave a blood trail in the hallway, because that would effect his or her ability to escape undiscovered for a few hours. Thats my theory for what it is worth, not much.
The fact that Mexicans were involved here explains why the police are clamming up AND the result will still be that Spring Break for Canadian College students in Cancun is finished. Mexico bites the big one here OR they catch the murderers and still bite the big one.
The Yucatan area is about to see a reduction in its tourist income, and the more the Mexican cops prevaricate, the worse it will be.