Transcript for Vanessa Guillen’s family says they’re being denied answers about her death: Part 1
The last 75 days for me, for my family, I haven't slept. Reporter: She's only 16 years old. But for three months now, since the disappearance of her sister, Lupe's life has been consumed by agony and fear. A nightmare. I would never in my lifetime think I should be fighting for my sister. Reporter: She first went missing from ft. Hood in April. She was eventually found brutally murdered. Her mother Gloria left to find comfort in her dreams. Does she talk to you in her dreams? Reporter: Tonight, a family's quest for justice. Launching a movement under the #iamvanessaguillen. She's like a sister for everyone now. Reporter: Vanessa's story now invoking outrage over sexual harassment and abuse in the military. How is it possible to go missing on base? On a military base? Reporter: Allegations that she was harassed by one of her own. Before she was murdered. This family, it's just like any family deserves answers. The lack of transparency through this whole process was despicable. She's going to be heard, and she's going to be remembered. Reporter: Does this make you feel good? What was she like? Soccer. Reporter: An athlete at heart, her family tells us, marathons were her passion. And even from a young age, one thing was clear. Vanessa's sense of duty to her country, the place where she was born and raised, the united States. High school prom? Reporter: She knew at 10 years old she wanted to go to the army? Reporter: When she turned 18, she signed with the army. You didn't want her to go. Reporter: She would eventually be assigned to ft. Hood, just hours away from her home in Houston, the place where they raised their six children. But then came that horrific day, April 22nd, when Vanessa suddenly disappeared. Her father tells me that same afternoon he felt a pain in his heart, something was just not right. Reporter: What do you think it was? Reporter: Vanessa had vanished without a trace. Her family became worried when Vanessa stopped responding to her older sister, Myra, drove to ft. Hood, but she arrived so late at night that she was turned away at the gate. She went back the following authorities told Myra, her sister's car keys, room key, I.D. And wallet were found in the armory room where she worked. But Vanessa was nowhere in sight. The military launching an investigation on april23rd. But Vanessa's family leaves ft. Hood with more questions than answers. Now looking back, Vanessa's mother tells me she started seeing changes in her daughter months before, as soon as she was stationed at ft. Hood. Reporter: She says she confronted her daughter, and Vanessa told her she was being sexually harassed by a superior, but she didn't report it, out of fear of retaliation. Reporter: So she never gave you a name. The army tells ABC news that they provide multiple avenues for reporting sexual misconduct, both within and outside the chain of command to ensure every soldier has the ability to seek help and has a safe work environment. For weeks, the guillens have been pleading for answers. The family's attorney accusing ft. Hood of keeping them in the dark. Was the military being forthcoming with information? Not at all. It was very, very concerning. When we asked the questions, who was Vanessa with that day? Who called her in? They wouldn't answer. They were very defensive about it. Vanessa would have had to check in at 5:00 A.M., 9:00 A.M., 3:00, and 4:00 P.M. Why did it require Myra to call you? You should know when she didn't check in. Reporter: Vanessa was last seen wearing a black tee shirt and purple leggings in the parking lot of her reggemental engineer squadron headquarters. The family desperate to find Vanessa alive, going public with their story, Myra delivering this message to her sister. Hold on, you're going to be back home. Reporter: The story of Vanessa's disappearance gaining attraction. She was sexually harassed. Reporter: Protesters gathering outside ft. Hood, demanding justice. Reporter: Two months after Guillen's disappearance, investigators would locate unidentified remains in bell county, Texas, about 20 miles away from the base. It's not confirmed yet whether it's my sister or not, but at this point, everything points to it. Reporter: The family continued to seek answers. The youngest sister's pain laid bare for the world to see. My sister's a human too! She deserves respect! She deserves to be heard! Because if this can happen to my sister, it can happen to any one else. Reporter: You're 16 years old? I'm 16. Reporter: Did you ever think you would be fighting like this? No one should be fighting for their sister's life. My sister was not safe. Reporter: On July 1st, the family would learn there was a suspect in Vanessa's disappearance. 20-year-old army specialist, Aaron Robinson. As officers attempted to make contact with the suspect, he produced a weapon and committed suicide by shooting himself. Reporter: When you found out that Robinson had killed himself, what did you think? That he was a coward. Reporter: A criminal complaint was filed against Robinson's alleged girlfriend, accused of covering up the she's revealed to investigators that Robinson told her he struck a female of soldier in the head with a hammer multiple times, killing her on ft. Hood, adding that Robinson then placed her in a box. Cecily Aguilar is now in jail, held without bond. She has pled not guilty to charges relating to helping dispose of Vanessa's body. At ft. Hood, the tomorrow army commander tells reporters the continuing investigation limits the amount of information he can provide. What I was able to share was tempered by my responsibility to protect the integrity of the investigation, so that we could, a, find Vanessa, B, prosecute those responsible for this I just wish I could have done a better job balancing those two needs. Reporter: The army tells ABC news that since Vanessa's disappearance, more than 500 soldiers and army criminal investigation command agents searched for her in ft. Hood and throughout central Texas. They add that Cid agents have conducted more than 300 interviews and are working closely with multiple agencies. Back in Houston, on July 5th, the Guillen family received the confirmation they had long dreaded. Hopefully it's not her. I pray to you, god, if it's not her, I'm going to do what I promised you. Reporter: Gloria says she can't bear to know the details of how her daughter was killed. You know the details. The whole thing, yeah. Reporter: Vanessa will be laid to rest later this month. Her mother telling us she expects a military funeral. It's what Vanessa would have wanted. Reporter: When we come back -- My sister will make history. Reporter: What the family says they're doing to make sure this never happens again.
This transcript has been automatically generated and may not be 100% accurate.