For more than a decade, “Lieutenant” Gregory Allen pumped up young military hopefuls at his gym in San Rafael, California. The bulky and bald-headed drill sergeant told war stories from his stint in Vietnam, collected donations, and even posed for photos in a U.S. Marines uniform with a Purple Heart and Bronze star.

The only problem: the Marine Corps says Allen, 67, never served. Now the wannabe jarhead is under investigation by the FBI and Department of Veterans Affairs for allegedly faking his entire military record.

The sham soldier’s fall from grace came last week, after one former Marine’s own detective work prompted the federal probe.

“He’s helping young people who want to join the Marine Corps, but he was doing it through lies and deception,” said James Brown, the watchdog who tipped off authorities.

Allen did not return e-mails or messages left at his gym or cellphone.

More than 100 young men and women have graduated from Allen’s House of Steel, a sweaty, no-nonsense gym in Marin County—known as one of the wealthiest and more liberal corners of America.

Some of Allen’s “recruits” stay with the regimen all through high school. In a March 29 post on the House of Steel Facebook page, “1Lt Gregory Allen” congratulates 18-year-old Chris Vogt, a member for five years, for shipping off to training in San Diego.

“He continues to help at the HOS with the daily functions,” Allen wrote. “Chris is like a son to me. I have watched him grow and become a great young man. God Bless Him and his Family.”

In a 2010 profile on House of Steel, Allen said civilians and aspiring military officers could only join the gym after a tryout. “Usually people off the street don't make it here,” Allen told the Marin Independent Journal. “They respond with fear and shock if they haven't been warned. We get one out of five who make it.”

The gruff, light-eyed Allen looks likes drill sergeant straight out of “Full Metal Jacket.” He played his part so well that he became the president of the Marin chapter of Military Officers Association of America. His gym-rat recruits served as the color guard and drill team at local events.

“He fooled a lot of us,” John Sammons, a past president of Marin’s Military Officers Association, told The Daily Beast. “He walked the walk, he talked the talk, he wore the uniform. There’s an honor [code]. Someone comes up to you and says, ‘I’m a former commissioned officer,’ we don’t ask for their [discharge papers].”

But Allen’s story publicly unraveled after a Bay Area TV reporter exposed his dubious military career Friday. He never served in the Marines or in Vietnam, and never received any medals, ABC 7 discovered through a records request.

Instead, the poser Marine enlisted in the Navy in 1968 but was discharged after eight months because of a knee injury that he sustained playing football prior to enlisting.

When ABC reporter Dan Noyes began probing Allen’s phony credentials, Allen told him to get off his property. “I'm done talking with you, partner, back up ... You’re down here to do a hit piece on this place,” Allen said.

Meanwhile Allen told a local newspaper asking about his service: “I’m not going to say anything. I’m going to let the lawyer answer these questions.”

Earlier this month, Allen asked clients not to answer questions from Noyes.

“My heart is troubled and with great sadness I must tell you that the House of Steel is under a vicious and vile assault from newscaster, Dan Noyes,” Allen wrote April 14. “Please do not talk to him. He has just enough information to get himself into trouble.”

Some supporters did heed Allen's warning. Early defenders told watchdogs that Allen does good things for the community and to leave him alone, said Brown, a former Marine who has outed other military fakers.

Brown teamed up with Noyes to investigate Allen. It all started when the sergeant major for the local Marines asked Brown if he knew who Allen was and why he was taking so much credit for helping young recruits.

Brown told The Daily Beast it wasn’t hard to poke holes in Allen’s story: pictures of the supposed lieutenant did the work for him. In one online photo, Allen stood next to the flag-draped casket of a fallen Marine, but the medals on Allen's red Marines blazer were out of order. (This Marine was mentored by Allen, and later committed suicide while in the service, Brown said.)

“He’s got a combat action ribbon above the Purple Heart and Bronze Star,” said Brown, a board member of the Wine Country Marines. “Anyone fresh out of boot camp would have known that was wrong. Veterans look at ribbons as resumes.”

In some photographs, Allen donned a Marine Corps Rifle Marksman badge, while in others he had a Rifle Expert badge. But Brown says a Marine can’t be both once you're a veteran. (“What you have qualified for when you get out of the service, is what you've got for life,” Brown said.)

Allen was also wearing a different number of ribbons in various photos.

The fake Marine couldn’t answer questions on the names of his boot camp, class or drill instructors, Brown said.

Adding to the pile of suspicion was the original name of Allen’s gym: “Fitness Boutique.” Brown says Allen transformed his business into a military-style stomping ground 10 years ago after fitness boot camps gained popularity.

Allen has a felony record to boot. He served a three-year prison sentence for violating a restraining order in 1997. According to the ABC7 report, Allen climbed to his wife’s bedroom window and threatened to cut her throat and shoot her.

Still, the faker was somehow able to obtain a VA medical card with Marines insignia and tooled around San Rafael with a veterans’ license plate with a Marine Corps emblem. He has a camouflage bumper sticker with the Marines battle cry, “OORAH!” above the words, “I love this job.”

The Department of Veterans Affairs told Brown that Allen’s card was valid, but that it was issued at a VA facility from out of state.

“He did enough research and enough study that he could fool the wealthy families that never served in Marin,” Brown said. “But he couldn’t get past the real Marine Corps.”

Veterans like Brown are infuriated by Allen’s charade. Once a troubled youth whose life was turned around by the Marines, Brown has dedicated his life to giving back to the Marines community and serves on the Palo Alto VA’s Veterans Focus Council, assists the VA with outreach, and organizes the Purple Heart Ceremonies and other events.

Brown said some of Allen’s recruits were inspired by the bogus lieutenant’s tales of being an elite Recon sniper. At least four of those recruits never made it home, Brown said.

“A lot of men joined the military based off the information he gave them, which was all lies,” Brown said. “Some joined special forces Recon, thinking their mentor served in Recon. Four of those young men ended up getting killed in combat.”

“I have to wonder if the experience they pulled from in those life and death moments were at all inspired by his lies and advice he provided to them based on fabrication,” Brown added. “Parents trusted their children with him, and he played God with their lives.”

It’s unclear whether Allen will be charged in violation of the Stolen Valor Act of 2013, which makes it a federal crime to fraudulently claim to have received military decorations in order to receive money. A local grocery store, United Markets, donated to House of Steel and touted its “generous fundraising support” for Allen's program in July 2013 circular. Another donor told ABC that he forked over $5,000 to Allen's Marine gym.

Last fall, House of Steel held an annual fundraiser at the Marin Yacht Club at $40 a ticket. The money was to go to shipping care packages to troops overseas and to fund Allen's gym program for Marines.

Brown says he alerted the FBI to Allen's "scheme" in an April 21 e-mail to David J. Johnson, special agent in charge of the bureau's San Francisco Division.

"He runs a for-profit business. A gym," Brown wrote of Allen. "And his scheme is that he's a decorated Marine Veteran, Special Forces and wears the uniform regularly to support this claim. He does not have a 501(C)3 but holds regular fundraising activities."

For Sammons, the allegations against Allen were heartbreaking. He wants to defend Allen’s work, as his acolytes often graduated at the top of their platoons.

He cannot, however, forgive the falsely-obtained bronze star medal, with a V for Valor, awarded for heroism during combat. Sammons has presented the American flag to fallen soldiers' next of kin.

“He stole my valor, yeah, sure, so be it on that one,” Sammons, who served as a Marine in Vietnam, told the Daily Beast. “But have you ever been to a military funeral? To me, stolen valor is any time someone is wearing something they don’t deserve. They have stolen the valor not only of the person that’s in the casket but every other person who’s been buried under that flag.”