Investigators may finally have a break in a cold case murder that has haunted the Boston area for almost 50 years.The Middlesex District Attorney's Office is slated to hold a press conference Tuesday afternoon to announce a "significant development" in the unsolved 1969 killing of Jane Britton due to DNA testing."Over the past year our office has been in the process of conducting DNA testing on the evidence taken from a 1969 Cambridge homicide," Middlesex District Attorney Marian Ryan said in a press release Monday.