KILLEEN, Texas (NewsNation Now) —  Fort Hood has faced a series of unexpected tragedies including homicides, suicides, off-duty accidents and training casualties this year, and now there are calls for an internal investigation.

Fort Hood is stationed in the heart of Texas and houses about 40,000 soldiers. Twelve soldiers this year alone have died in events unrelated to combat.

“I can understand harm out there in the battlefield,” said Rep. Henry Cuellar (D-Laredo). “But when they’re back home in a Texas city or somewhere else there’s a problem.”

The latest death was 25-year-old U.S. Army Private and Navajo Nation member Carlton Chee. He passed away last week after collapsing during a training excerise.

The Navajo Nation Council is calling for an investigation saying “if there is any malfeasance or negligence involved, the Navajo nation calls on our national leaders to pursue every available avenue to protect the lives of our Navajo warriors and those serving in the U.S. armed forces.”

On Monday, crowds gathered in Austin to rally in support of the dead soliders and the “I am Vanessa Guillen Bill.”

“Fort Hood has to be held accountable,” said Mayra Guillen, sister of Vanessa Guillen. “Their leadership has to be held accountable.”

The dismembered remains of 20-year-old Guillen were found in a shallow grave in June as she was preparing to file a sexual harassment claim against her accused killer. Her case drew national attention and action from the president.

“The FBI and the DOJ are now involved, we got them involved,” said President Donald Trump. “And the people at Fort Hood where it took place are very much involved. We didn’t want this swept under the rug, which could happen.”

Just last week, the army removed its Senior Commander at Fort Hood and launched a two-week civilian investigation into the base’s culture and climate. Some lawmakers called the move critical.

“There’s great diversity in the lower ranks,” said Rep. Veronica Escobar (D-El Paso). “But you begin to look at the names and profiles at the higher ranks and it is not as diverse as it needs to be.”

“Our young men and women who volunteer to serve in our military deserve far better than this,” said Sen. John Cornyn (R-Texas). “And this is just simply unacceptable.”

The internal investigation team is made up of five civilian members. Cornyn said a Senate committee will review the findings then come up with a plan of action. Fort Hood has not responded to NewsNation’s request for comment.