SALEM – The last inmate involved in the June 2007 violent melee at the Middleton Jail has pleaded guilty.Raul Carraquillo, also known as Raul Llanos, 35, formerly of Lawrence, changed his plea to guilty Thursday afternoon in Salem Superior Court, confessing to assault and battery with a dangerous weapon, assault and battery with a dangerous weapon causing serious injury, assault with a dangerous weapon and destruction of property before Judge David A. Lowy.He will serve 30 months in state prison before being placed on probation for five years.Assistant District Attorney Michael A. Patten said the incident involved seven Middleton inmates, confined to the high-security segregation unit. The inmates were showering shortly after midnight on June 7 when they crawled out from underneath the shower doors and attacked two guards in the unit with brooms and mop handles taken from the utility closet.Other correctional officers quickly responded and subdued the inmates in less than five minutes.At the time, Carraquillo was about to get out of jail after serving his punishment on an unrelated case.Patten said that Carraquillo was one of the “least culpable” in the case, but that he was a participant.While on probation, Carraquillo will be evaluated for drug treatment and counseling, random screenings, have a job or have five pending job applications on file.