A 20-year-old U.S. Marine was killed during an active-duty training exercise in California when a gun reportedly discharged in a truck filled with other service members.

Lance Cpl. Jackson J. Forringer, with the 2nd Marine Regiment based in Camp Lejeune, North Carolina, died on April 20 "while conducting training during Integrated Training Exercise 3-23 at Marine Corps Air Ground Combat Center, Twentynine Palms, California," 2nd Lt. Olivia Giarrizzo, a spokesperson for the 2nd Marine Division, said in an email to Fox News Digital on Wednesday.

"The incident is currently under investigation by NCIS. No other injuries were reported," Giarrizzo added.

The spokesperson cited an active investigation by the NCIS (Naval Criminal Investigative Service) and declined to go into further detail.

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Marine veteran Trey Smith-Tatham, who previously served with Forringer, said Forringer was killed "by an inadvertent gun discharge while he was with other Marines in the back of a Medium Tactical Vehicle Replacement, or 7-ton truck," according to Corps Marine Times.

Smith-Tatham, 21, told the outlet that Forringer, an infantryman, arrived with his unit in Twentynine Palms for pre-deployment training in late March.

Marine scout sniper training Camp Lejeune

U.S. Marines with the 2nd Battalion, 2nd Marine Regiment, 2nd Marine Division, fire at targets at Camp Lejeune, North Carolina, on Oct. 13, 2022. A member of the same unit died during a training exercise in California on April 20, 2023. (U.S. Marine Corps)

Smith-Tatham, who said he was discharged in 2022 due to drug use but kept in touch with members of his former unit daily, told the outlet he learned that Marines from Forringer’s platoon had been ordered into the back of the truck. He said they had been told to set their service rifles at "condition one," meaning with a loaded magazine and a round in the chamber.

It's unclear how Forringer was shot, but Smith-Tatham said he believes someone in the vehicle, which was not moving at the time, had their weapon's safety off.

Smith-Tatham said he lost a close friend, Pfc. Zachary Riffle, who was killed along with a second Marine in a seven-ton truck rollover at Camp Lejeune in January 2022, and he recalled Forringer as a friendly and positive person who invited him along on gym workouts after Riffle's passing to show moral support.

"He was just a really good dude," Smith-Tatham said of Forringer.

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Lance Cpl. Jackson J. Forringer official photo

Lance Cpl. Jackson J. Forringer, 20, died during a training exercise in Twentynine Palms, California. (U.S. Marine Corps 2nd Marine Division)

Forringer died just weeks after three Camp Lejeune Marines were injured in a separate all-terrain vehicle crash at Twentynine Palms.

The Marine who had been driving the vehicle during the rollover crash that killed Riffle was acquitted on charges that included manslaughter and negligent homicide earlier this month.

Twentynine Palms training exercise

Marines train in a simulated Iraqi village at the Twentynine Palms Marine base on Nov. 14, 2005, in California. Lance Cpl. Jackson J. Forringer died during a training exercise at the same base. (David McNew / Getty Images)

"It’s hard to be this age and lose as many friends as we have when we all joined when we were, like, 19 years old," Smith-Tatham said. "We shouldn’t be losing friends this young without any clarity or reason behind it."

Forringer, of Chesnee, South Carolina, was honored in an obituary shared online by his parents, saying he "met Jesus" in an "active-duty training" at Twentynine Palms.

Twentynine Palms Marines simulation

The Twentynine Palms Marine base is seen on Nov. 14, 2005. Lance Cpl. Jackson J. Forringer died during a training exercise at the same base. (David McNew / Getty Images)

"Born April 9, 2003 in Anderson, SC. he was a son of Todd A. Forringer and Andrea L. Forringer of Chesnee, SC. Jackson was a 2021 graduate of Chesnee High School and was actively serving in the United States Marine Corps, a lifelong dream. He never met a stranger and was one of the humblest, kind-spirited individuals you could meet. He loved to give back and help others," the obituary shared on the Harris-Nadeau Mortuary website reads. "Jackson loved his family and his friends unconditionally and had an extra special bond with his cousin Kate."

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In May 2021, the family was featured in a Mother's Day piece by the Spartanburg Herald-Journal celebrating Forringer's formal adoption narrowly made official before his 18th birthday. Jackson Forringer had come to live with the family as a teenager after having entered the foster care system at age 5 and having lived in nearly two dozen other homes.

"Jackson was just part of the family from day one," Todd Forringer told the paper at the time.