A Marine from Crowley, fatally shot this week at Camp Lejeune, N.C., had overcome physical hurdles to join his brothers in the Marine Corps, his twin brother said Thursday.Lance Cpl. Mark N. Boterf, 21, was shot in the chest while on sentry duty Tuesday at the main entrance to the base, the Marine Corps said in a statement late Wednesday. Military officials said the shooting is still being investigated but appears accidental. After graduating from Crowley High School, Boterf had surgery to correct a hernia, then pushed himself to pass the fitness tests required by the Marines, his twin, Michael Boterf, told The Associated Press.“He excelled at the [physical] standards. It is three pullups; he could do 20. To be able to do that, so quickly after surgery, he made an example,” Michael Boterf said.Father Aubrey Boterf said Mark Boterf had a “giving heart, was a cheerful person and loved God.” His older brother, Joseph Boterf, is also a Marine. He was with his parents in Crowley on Thursday when they read a statement to reporters.Relatives declined to discuss the shooting because it is still under investigation. Instead, they talked about the young Marine’s character. They were told that he was on duty that day because he volunteered to take a shift for a fellow Marine who was on leave to get married. “He would do anything for anyone,” Michael Boterf said. “No matter what it was, if you needed it, he’d do it for you.” The second and third of seven brothers and three sisters, Mark and Michael Boterf were born in Amory, Miss., but moved to Crowley in 2012, where they attended their senior year and graduated.Anthony Kirchner, a spokesman for the Crowley school district, said faculty, staff and students were deeply saddened by the Marine’s death.“We are very grateful for his service to our country, and we join his family and friends in mourning this tragic loss,” Kirchner said.‘Great Christian people’Great-grandmother Norma Jividen of Burleson said Mark Boterf’s offer to take a shift for a fellow serviceman “was his character.”“The whole family is that way,” she said. “They’re just great Christian people, and he was just a good person.”Mark Boterf was assigned to the 2nd Radio Battalion, II Marine Expeditionary Force Headquarters Group at Camp Lejeune, according to a Marine Corps news release. He was temporarily assigned to a support battalion as a sentry.He had also served as a special intelligence system communicator and was promoted to lance corporal in October.Boterf had not been deployed overseas, but he had earned commendations including the Global War on Terrorism Service Medal and the National Defense Service Medal. Boterf was shot in the chest in a guard shack at the main base entrance, authorities said. Indications are that a “negligent discharge” caused his death, a Defense Department spokesman said Wednesday.The Marine who fired a single shot from an M4 rifle remained in custody while the Naval Criminal Investigative Service reviews the incident. He hasn’t been identified. Other guards were at the gate, but no one else was hurt, officials said.“It appears right now to have been an accident,” Army Col. Steven Warren, a Defense Department spokesman, told reporters Wednesday.Base spokesman Nat Fahy said confirming that the shooting was accidental will take several weeks of examination. Staff writer Bill Miller contributed to this report, which includes material from The Associated Press.