Police unions represent people who arrest thieves, not employ them. In Somerville, Mass., they’ve got both types. Last week, a source close to the local police department in Somerville, adjacent to Boston’s Charlestown neighborhood, revealed that the Somerville Police Employees Association (SPEA), an independent union of nearly 100 patrol officers, is missing between $50,000 and $90,000 from its coffers and that the culprit is one of its own. SPEA President Michael McGrath indicated that the case is under investigation, but would not comment further. No outside government agencies have gotten involved yet, but that could change soon.