X-link to the DRM-free thread for Dreamspinner Press' 10th anniversary flash giveaway freebie, available worldwide until 12 PM Eastern Time:
Murder Most Gay by John Simpson, 1st in his eponymous series of police procedural murder mysteries with m/m romantic elements, starring a pair of gay cops who are professional partners who eventually establish personal relationships with other men. This 1st installment pits them vs a serial killer who is targeting gay men.
ETA: apparently the author is a former police officer, and this case is loosely based on a real life one he investigated back in the 1980s.