CAMP LEJEUNE, ONSLOW COUNTY -

Camp Lejeune has formally released the identity of the Marine sentry fatally shot by another Marine at the base's main gate Tuesday.

The deceased victim has been identified as 21-year-old LCpl. Mark N. Boterf, of Crowley, Texas, according to a Camp Lejeune statement released late Wednesday night.

The Daily Journal in Mississippi reports Boterf went to Tupelo High School in Tupelo, Miss. His twin brother, Mike, is also a Marine.

Camp Lejeune Director of Public Affairs Nat Fahy said Boterf was shot when another Marine sentry discharged his M4 rifle while the two were inside the guard shack of Camp Lejeune's main gate. The shooting happened at about 5:30 p.m. Tuesday.

Boterf suffered a gunshot wound to the chest and was pronounced dead about 40 minutes later at Naval Hospital Camp Lejeune, Fahy said.

Boterf was originally assigned to 2nd Radio Battalion aboard Camp Lejeune. He was then temporarily assigned to Headquarters and Support Battalion as a Marine sentry, base officials said.

Boterf's twin brother told The Daily Journal that Boterf was a gate sentry because he volunteered so another Marine could take a leave and get married.

Based on initial assessment, the NCIS has determined that the fatal shooting was the result of a "negligent discharge" of the M4 rifle, Fahy said.

"However, it will take several weeks of forensic examination to confirm this with absolute certainty," Fahy stated in a release.

At last check, the shooter was still in custody being questioned. His identity is being withheld.

Boterf joined the Marine Corps in August 2012, according to Camp Lejeune. He joined 2nd Radio Battalion in 2013, served as a special intelligence system communicator, and was promoted to lance corporal on Oct. 1, 2013.

Boterf's awards include the Global War on Terrorism Service Medal and the National Defense Service Medal, Camp Lejeune stated. He had no history of deployment.

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A "negligent discharge" of a rifle by a Marine guard likely caused the shooting death of a fellow Marine at Camp Lejeune's main gate, investigators said.

According to Nat Fahy, director of public affairs at Camp Lejeune, it will take several weeks of forensic examination to confirm. But based on initial assessment by NCIS officials,Tuesday afternoon's fatal shooting was "likely caused by a negligent discharge."

Fahy said the fatal shooting happened at about 5:30 p.m. Tuesday inside the guard shack at the Camp Lejeune main gate. A Marine guard discharged an M4 rifle, causing a gunshot wound to the chest on another Marine guard.

First responders tried to revive the Marine, but the victim was pronounced dead at 6:10 p.m. Tuesday at Naval Hospital Camp Lejeune, Fahy said. The victim's identity is being withheld pending the notification of family.

"I ask you that your hearts and prayers go out to the family and to the community as a whole-- to the Marines and all our civilian Marines who work on this base, and all of the Onslow County community," said Brig. Gen. Robert F. Castellvi, the base commander of Camp Lejeune. "It's a tough loss for us and we'll get through it as a community."

(CLICK HERE: Full remarks from Brig. Gen. Robert F. Castellvi, courtesy of Camp Lejeune.)

Base officials said the male shooter remains in custody as of Wednesday morning. But his identity has not been released.

"I can't imagine how that Marine may feel, and how other Marines may feel knowing that this happened right here," said Gunnery Sgt. Julian Johnson, an active-duty Marine. "It's just a sad day for us all."

Fahy said Camp Lejeune was never put on lockdown because it was an isolated incident.

(CLICK HERE: Full interview with Dir. of Public Affairs Nat Fahy.)

No other details are available at this time. Refresh this page for more information as they become available.