The case against Long Island’s suspected Gilgo Beach serial killer has emerged as a potentially precedent-setting battleground in the use of advanced DNA techniques in criminal cases. A New York judge is weighing whether to allow certain DNA evidence into the forthcoming murder trial of Rex Heuermann. Prosecutors say DNA extracted from hair fragments recovered from the bodies of victims overwhelmingly implicate the Manhattan architect. But Heuermann’s lawyers argue the analytic methods used on those samples are unproven. Experts say the case could mark the first time such techniques are allowed as evidence in a New York court.