I've counted 11 since January, including this one, and 8 near misses. The 8 misses include those who were shot at, those who were wounded, and those who were wounded and later killed in a second attempt.
You are right, Dan. This is no longer the Cozumel we once knew. It is not just the drug-related murders, it also a pile of other bad changes. Rampant burglaries, crooked cops, inept government officials (well, maybe that one is not so new), new laws and policies hard on small businesses, the loss of trees in the city, the 14,000 tourists a day and their garbage, the huge amount of trash floating to Cozumel from countries to the south, the seaweed, the reefs' decline, the loss of public beaches, the loss of restaurants serving the old style Cozumel cuisine (think Tortas Moros, El Portal, etc.), lack of parking, soooo many bad drivers, the hideous and poorly-designed ferry pier, the proliferation of taxis and their lackadaisical attitude towards courtesy and traffic laws, the gauntlet of touts you have to pass on the malecon, the loss of the feeling of "community" there was before so much immigration from other Mexican states, loss of airline connections due to competition with Cancun airport, and more...
On the good side, there are now hospitals and clinics, decent dentists, large grocery stores, well-stocked hardware stores, FEDEX and other delivery services, much fewer black spiny sea urchins, reliable electricity, fast ferries, car ferries that go to Calica instead of Puerto Morelos... I am sure there are more good changes that came to Cozumel, but I can't think of them right now.