An armed man suspected of robbing four McDonald’s restaurants since last year is in custody. Sean Martin, 23, was arrested Thursday by Spokane County sheriff’s detectives on three counts of first-degree robbery, authorities said. He also has been implicated in a McDonald’s robbery in Colville last year but currently is charged only with the holdups that occurred within Spokane County. At the time of his arrest, Martin was armed and in possession of a large quantity of ammunition, according to the Sheriff’s Office. Officers also seized money from Martin’s home and vehicle. The investigation, led by sheriff’s Detective Kirk Keyser, linked Martin to robberies of McDonald’s restaurants at 6321 N. Monroe on May 14, and at a Cheney franchise on May 21, as well as a May 3, 2012 robbery at the 1818 N. Monroe franchise. In addition to the sheriff’s office, Cheney police and the U.S. Marshal’s were involved in the investigation.