An 18-year-old American woman has been identified as one of the five people killed early Monday when a gunman opened fire at a nightclub in the Mexican resort town of Playa del Carmen. Robert Martinez confirmed to NBC News that his sister, Alejandra Villanueva, perished in the early-morning siege. The Denver resident was on vacation with a friend when a gunman opened fire at around 2:30 a.m., after being denied entrance to the BPM electronic-music festival taking place inside the Blue Parrot nightclub. Quintana Roo’s attorney general, Miguel Angel Pech, said in a statement that four male victims were killed by gunshot and one woman was killed in the stampede that resulted from clubgoers fleeing the violence. The other victims included two Canadians, one Italian, and one Colombian, according to Mexican officials.