(CNN) Fort Hood Pfc. Vanessa Guillen was bludgeoned to death with a hammer in the armory room where she worked, an attorney for Guillen's family said on Thursday.
Guillen's body was transported from the military installation by her killer, attorney Natalie Khawam told CNN, citing details the family learned during a meeting with Army investigators on Wednesday night.
The main suspect in disappearance was identified by officials on Thursday as Spc. Aaron David Robinson.
Khawam said the family told her that Guillen had planned to file a harassment complaint against Robinson the day after she was killed, and that they believe Robinson became enraged when she told him that.
Fort Hood officials said they were not aware of reports of sexual harassment involving Robinson but the investigation was ongoing.
Robinson, 20, killed himself on Wednesday after police confronted him in Killeen, according to US Army Criminal Investigation Command, which calls itself CID. He fled Fort Hood late on Tuesday.
"While law enforcement agencies attempted to make contact with the suspect in Killeen, Texas, Specialist Robinson displayed a weapon and took his own life," CID Senior Special Agent Damon Phelps said at a news conference on Thursday.
Robinson and Guillen, though co-workers, were located in different buildings; he was not in her line of command, Phelps said.
Robinson "was not in CID custody" at the time he fled the installation.
Phelps said investigators were looking into Robinson's interactions with Guillen. He said there was "no credible information" Guillen had been sexually harassed or assaulted. He said investigators had conducted more than 300 interviews in the case.
Robinson, from Illinois, entered the Army in October 2017.
Khawam said investigators told the family that Robinson called a woman he was involved with to help him dispose of Guillen's body after moving it outside the base.
Texas Rangers also arrested a civilian suspect in connection with Guillen's disappearance, according to CID.
The suspect has been identified as Cecily Anne Aguilar, the estranged wife of a former soldier from Fort Hood. She is in Bell County Jail awaiting civilian authorities to press charges, CID said.
Guillen, 20, was last seen in the parking lot of her barracks at the Texas Army base on April 22, CID said.
Senior members of CID Command met with Guillen's family on Wednesday, Phelps said.
Before Guillen went missing, she told her family that she was being sexually harassed by one of her sergeants at Fort Hood, according to a website her family set up to promote the search. The sergeant wasn't identified.
Early Wednesday, US Marshals, Killeen police and the Lone Star Fugitive Task Force located the soldier suspected in Guillen's disappearance, CID said. He had left his Fort Hood post. The authorities confronted him walking along a commercial and residential thoroughfare on the northeast side of the city, a few miles from base.
"As officers attempted to make contact with the suspect, the suspect displayed a weapon and discharged it toward himself. The suspect succumbed from a self-inflicted gunshot wound," the Killeen Police Department said in a news release.
On Wednesday, Guillen's sister Mayra said she had met the soldier suspected in the disappearance of her sister.
"When I first went up to that base, that subject, I met him, not knowing that he had something to do with it. I felt something was telling me that he did something, and I wasn't wrong apparently," Mayra Guillen said. "And apparently now, he kills himself. Why? I don't know."
"But whoever is responsible has to pay, and we demand a congressional investigation," she added.
This came just hours after investigators discovered on Tuesday the partial remains of a body near the Leon River in rural Bell County, where Killeen is located.
While authorities have not confirmed it, Guillen's family believes the remains belong to their missing loved one, they said at a news conference.
Phelps said the remains have not been positively identified. The investigation into Guillen's disappearance is separate from another into her family's claim that she was sexually harassed.
The remains were found in a shallow grave, and search operations were suspended, pending identification, said Tim Miller, the director and founder of Texas EquuSearch.
Due to her time in service, Guillen was promoted to specialist on Wednesday, according to the Fort Hood website.
Authorities discovered the remains about 26 miles from the site where on June 19 investigators found the body of Pvt. 2nd Class Gregory Wedel-Morales, who went missing last year while driving in Killeen.
He was scheduled to be discharged within days of his disappearance, the Army said.
It's unclear whether there's a connection between Guillen and Wedel-Morales, but Army investigators say there is "no credible information" linking the cases.
Foul play is also suspected in Wedel-Morales' death, and the Army is offering a $25,000 reward for information. The Army, League of United Latin American Citizens and Houston rapper Baby Bash have pooled together a $55,000 reward for information on Guillen's disappearance.
After Guillen went missing in April, her car keys, room key, identification card and wallet were found in an armory room where she was working that day.
"Our hearts are broken. We feel pain, frustration and devastation. This shouldn't have happened. We demand a congressional investigation. We demand the truth," Khawam said in a statement.
"If this could happen to Vanessa, this can happen to any one of our sisters, daughters and mothers. There's no reason why a young beautiful girl who joined the Army, to honorably serve our country, should be in a shallow grave near on our own turf."