A routine stop conducted by the Sag Harbor Village harbormaster led police to discover the village had been swindled out of $12,000 in boat dockage fees, Village Chief Austin J. McGuire said Monday.Matthew F. Keller, 41, a resident of the village, is accused of filing fraudulent documents with the village clerk in order to obtain reduced resident dockage fees for an acquaintance of his who has not lived in Sag Harbor since 2014. Bob Bori, the harbormaster, stopped the acquaintance on the water recently for a violation. “He became suspicious when the boat was registered outside the village and he knew it was docked at a village slip,” Chief McGuire said. “He pulled the paperwork and found a copy of the registration, which had been forged to include the defendant [Mr. Keller] and a village address.” Police culled through all the paperwork on the boat, a 1973 Boston Whaler, back to 2013. All the documents had forged registrations, Chief McGuire said, leading to a charge for each of the last five years. The offense committed in 2013 is outside the statute of limitations, he said.The village lost over $12,000 in revenue, according to the chief. Asked why the boat owner himself was not charged, Chief McGuire said it was Mr. Keller who submitted the paperwork to the village by email. The acquaintance, whose name was not released, was “uncooperative,” he said. Mr. Keller was charged on Friday with a total of 10 felonies, five counts of offering a false instrument for filing and five more for falsifying business records in the first degree. He was released on $1,000 bail. “We are reviewing all of boat paperwork to see if this is a systemic problem,” Chief McGuire said. The New York State Department of Motor Vehicles Division of Field Investigation assisted village police in this investigation.