SALEM – An internal investigation has been launched into Friday’s arrest of a Swampscott man during a large fight in Lappen Park.A bystander videotaped the 1 a.m. arrest and placed the footage on YouTube.com.The title of the video is, “Bad Salem Cop” and the 39 second video shows an officer grabbing Travis Markarian, 21, of 22 Nason Road, Swampscott, by the throat before taking him into custody.The officer in question is reportedly Patrolman Larry Puelo, who has been placed on internal duties pending the outcome of a department investigation.A Salem police lieutenant confirmed Monday that an investigation was under way because of the YouTube video.”It’s the result of a video that is on YouTube,” Lt. Scott Englehardt said. “As a result of the video, Internal Affairs is going to investigate to see if any violations were made in the department’s policy.”Markarian was one of four people arrested after a fight broke out around the closing time of local bars.One officer was kicked and grabbed while another was allegedly punched in the face by Michael Wermuth, 21, of 73 Mostyn St., Swampscott, who was arrested.The other two suspects arrested were identified as Thomas Mattson, 25, of Beverly and Christopher Burke, 21, of 11 Banks Road, Swampscott.Their charges range from assault and battery on a police officer to failure to disperse.