MALVERN, Pa. (AP) — The remains of dozens of 19th-century railroad workers from Ireland will stay undisturbed in a mass grave near Philadelphia.Local researchers say they have ended their efforts to unearth, identify and properly rebury the immigrants, who died after a cholera outbreak in 1832.Historians Bill and Frank Watson believe they have found the grave in woods near Malvern, but it's too close to active train tracks to excavate.The brothers have worked nearly a decade on their Duffy's Cut Project to discover what happened to 57 laborers who helped build the Philadelphia and Columbia Railroad.They believe many died of cholera, but others were killed by vigilantes driven by prejudice or fear of disease.Some human remains recovered outside the mass grave seem to confirm their theory.