A discarded cigarette found near the body of a 24-year-old Vermont school teacher in her apartment nearly 52 years ago helped lead investigators to an upstairs neighbor who they say strangled her after having a fight with his wife, police said Tuesday. Burlington Police DNA evidence collected from the cigarette butt and dogged investigative work led authorities to the man they say killed Rira Curran within a 70-minute window on a July night in 1971. The suspect, identified as William DeRoos, who was 31 at the time, had left his apartment that night for “a cool down walk.”