At a press conference Wednesday, Guillen family attorney Natalie Khawam made the connection while blasting the U.S. Army for its handling of the case.
"We lost a life. We lost a beautiful young soldier," Khawam said. "Enough is enough."
The event comes on the day after human remains were found in central Texas during a search for Guillen. Guillen's family members believe the remains belong to her.
Guillen's sister, Mayra, said she met the man who died by suicide, who was later identified by authorities as a suspect in the case.
"I met him not knowing that he had something to do with it," Mayra Guillen said. "I felt something was telling me that he did something and I wasn't wrong apparently. He still had the nerve that day to laugh in my face. And apparently now, he kills himself. Why? I don't know. But whoever is responsible has to pay and we demand a Congressional investigation."
A civilian was also in custody related to the case, according to Killeen police.
As the family spoke in Washington, the U.S. Army Criminal Investigation Command released a statement:
"The person who took his own life earlier today in Killeen after being sought by Killeen police and federal marshals was a soldier from Fort Hood and had fled the base earlier in the day. A civilian has been arrested in connection with Vanessa Guillen's disappearance. The civilian suspect is the estranged wife of a former Fort Hood Soldier and is currently in custody in the Bell County Jail awaiting charges by civilian authorities."
Guillen reported that she was the victim of sexual harassment prior to her disappearance.
"We stand here for justice. We stand here for Vanessa," Khawan said. "We stand here for every service member who suffered harassment and didn't feel safe reporting it."
Vanessa's younger sister, Lupe accused the Army of covering up the case as the search continued.
"They lied to our faces every single day," Lupe Guillen said. "How can this happen on a military base while she was on duty?"
Texas EquuSearch founder Tim Miller told ABC13 on Sunday, "The search for Vanessa is now over."
As family members gathered in Washington, investigators in Killeen were looking for answers after the person of interest died by suicide Wednesday morning when authorities tried to make contact with them.
Guillen, who is from Houston, had been missing since April 22.
Miller had been involved with the search during recent weeks. He said the remains were found very close to where they discovered evidence last week in the Leon River. He described the discovery as a "shallow grave."
"It's believed to be her ... pending positive identification which that will have to be determined by the medical examiner's office, but I'm confident to say the search for Vanessa is now over," said Miller.
Last week, they said foul play was suspected in Guillen's disappearance.
Guillen grew up in southeast Houston, graduated from Cesar Chavez High School, played soccer, and loves the Puerto Rican singer Bad Bunny.
Guillen was last seen on April 22 at 1 p.m. in the parking lot of her Regimental Engineer Squadron Headquarters, 3rd Cavalry Regiment.
Her car keys, barracks room key, ID and wallet were found in the armory room where she was working earlier in the day, but her cell phone has not been recovered.
Khawam said she's discovered at least two alleged incidents of sexual harassment -- a superior walking in on Guillen showering and another verbally assaulting her with vulgar remarks in Spanish. She says the person who died by suicide was the superior in the shower incident.
Khawam said Guillen told loved ones she didn't want to report the sexual harassment out of fear of retaliation.
"The facts aren't good. I don't like them," said Khawam. "There were a few incidents where she had told her colleagues, her friends, her family about being sexually harassed but she was afraid to report it. How does someone disappear on a base that has more protection and safeguards than anyone else on the planet?"
The Army's Criminal Investigation Command launched an investigation into allegations that Guillen was sexually harassed.
"I opened an investigation concerning the information provided by the Guillen Family that Pfc. Vanessa Guillen was harassed prior to her disappearance," said Commander of the 3rd Cavalry Regiment Col. Ralph Overland. "I take allegations of sexual harassment very seriously and we are conducting a thorough investigation."
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