Prosecutors have announced a charge in the case of Pfc. Vanessa Guillen, an Army soldier whose family had searched desperately for answers since she disappeared in April, detailing for the first time accusations that she was killed by another soldier who then tried to dispose of her remains.

In a federal complaint, the accused soldier was identified in early July as U.S. Army Specialist Aaron Robinson, 20, who killed himself with a pistol a few days earlier as the police approached.

The authorities also arrested Specialist Robinson’s girlfriend, Cecily Aguilar, in Killeen, Texas. Justice Department officials said in court documents that Specialist Robinson told Ms. Aguilar that he repeatedly struck Private Guillen on the head with a hammer, killing her, and hid her body in a large box. The couple then tried to dismember and burn the remains, according to the complaint.

If Ms. Aguilar is convicted of the charge against her, conspiracy to tamper with evidence, she faces a maximum sentence of 20 years. It was not immediately clear whether she had a lawyer.

The family of Private Guillen has been demanding answers since she disappeared on April 22. As weeks went by with no apparent progress in the search, her case captured the attention of state leaders, celebrities and activists who have linked her story to the problem of sexual harassment in the military.

“We owe it to those who put on the uniform, and to their families, to put an end to sexual harassment and assault in the military, and hold perpetrators accountable,” former Vice President Joseph R. Biden Jr. said on Friday in a statement expressing sympathy for Private Guillen’s family.

Here is what we know about the case.

Where was Private Guillen last seen?

Private Guillen, 20, was last seen in the parking lot of her Regimental Engineer Squadron Headquarters at Fort Hood, wearing a black T-shirt and purple workout pants, between 11:30 a.m. and 12:30 p.m. on April 22. Investigators who searched her phone found that the last person she texted was Specialist Robinson.

Specialist Robinson worked in a building at Fort Hood that was adjacent to where Private Guillen worked, according to Special Agent Damon Phelps of the Criminal Investigation Command. He was not Private Guillen’s superior and not in her chain of command, Mr. Phelps said at a news conference on July 2.

A witness told investigators that Private Guillen left the arms room where she had been working and went to the arms room controlled by Specialist Robinson to confirm serial numbers for weapons and equipment, the complaint said.

Specialist Robinson later said he read her the serial numbers and gave her paperwork, according to court documents. He said he believed she then left to go to the motor pool.

Two witnesses later said that on April 22, they saw Specialist Robinson coming out of the arms room, pulling a large “tough box” with wheels “that appeared very heavy in weight,” according to the complaint.

Specialist Robinson loaded the box into his vehicle and drove away, the witnesses said.

How has the search unfolded?

Private Guillen was reported missing around April 23.

Her car keys, barracks room key, ID and wallet were found in the armory room where she had been repairing small arms and artillery.

On April 24, the U.S. Army Criminal Investigation Command posted a news release asking for the public’s help in finding her.

More than 500 soldiers have searched for Private Guillen in buildings, barracks, fields, training areas, lakes and trails at Fort Hood, an area that a spokesman compared to the size of New York City. Aircraft from the 1st Cavalry Division have flown more than 100 hours to help in the search, and more than 150 people were interviewed, the authorities said.

On July 1, the Army announced that an arrest had been made in connection with the case and that a suspect had killed himself.

Fort Hood officials also said that, because of her time in service, Ms. Guillen had been promoted to specialist, effective July 1.

The family says she was sexually harassed.

Private Guillen told friends and fellow soldiers at her base that she had been sexually harassed, according to Natalie Khawam, a lawyer for the private’s family.

In June, officials at Fort Hood announced that they had appointed a team to investigate those accusations.

“My sister Vanessa Guillen was sexually harassed yet nothing was done,” her sister Lupe Guillen said at a news conference on July 1. “She deserves respect. She deserves to be heard because if this can happen to my sister, it can happen to anyone else.”

Before federal prosecutors announced the charge against Ms. Aguilar, Senator Kirsten Gillibrand of New York and Representative Jackie Speier of California, both Democrats, sent a letter to the Department of Defense’s acting inspector general calling for an investigation.

“The disappearance of Specialist Vanessa Guillen raises serious and alarming questions about the Army’s ability to prevent sexual harassment and assault, respond to criminal acts and provide justice for victims and their families,” Ms. Gillibrand said in a statement.

Mr. Phelps, the special agent, said that there was no credible information to suggest that Specialist Robinson had sexually harassed Private Guillen.

“If anyone does have credible information to corroborate these allegations, we strongly urge them to come forward and report to us, or to their chain of command,” he said.

Ms. Khawam also called for legislation in Private Guillen’s name that would establish better protocols regarding sexual harassment and assault, like allowing members of the military to make reports through a third party rather than having to do so through the chain of command.





Missing Fort Hood Soldier’s Remains May Have Been Found

A lawyer for the family of Pfc. Vanessa Guillen said on Wednesday that her remains had most likely been found and that a suspect in her disappearance had killed himself.

“As you know, there has been a lot of updates since we last spoke. We believe that her remains were found. We believe that the suspect had killed himself in the morning, and that unfortunately doesn’t provide us much information about how this happened, why this happened. And we believe that the person that killed her is that person that sexually harassed her, the one that walked into the shower. So, you know, this, again, shouldn’t have happened. And now she’s not with us.” “Just say the hashtag, #IamVanessaGuillen. All those men and women in our service suffering from sexual harassment, suffering from sexual assault — because they report it — yet they take it as a joke. My sister’s no joke. My sister’s a human being. And I want justice, and I want answers.”

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A lawyer for the family of Pfc. Vanessa Guillen said on Wednesday that her remains had most likely been found and that a suspect in her disappearance had killed himself.

The authorities have not confirmed the identity of the remains.

On June 30, partial human remains were found near the Leon River in Bell County, Texas, and were sent to be processed by the Texas Rangers, the Army Criminal Investigation Command and other agencies. The identification of the remains is pending.

Ms. Khawam said that the family believed Private Guillen’s remains had been found. “At this point, everything points to it,” said Mayra Guillen, one of the private’s sisters.

Lupe Guillen, however, said at the time that because the remains had not yet been conclusively identified, “I still don’t lose hope.”

The accusations against Ms. Aguilar.

At the time Private Guillen disappeared, Ms. Aguilar, 22, was living with Specialist Robinson, according to the complaint.

Prosecutors said in court documents that she initially lied to investigators about what she knew but on June 30 confessed to playing a role in the attempted disposal of the private’s body.

Ms. Aguilar told investigators that Specialist Robinson had picked her up late on April 22 or early on April 23 at the gas station where she worked.

He drove her to an area near the Leon River, where he had left the box and then showed her the body, according to the complaint.

Ms. Aguilar said she helped Specialist Robinson dismember the body with an ax or hatchet and a machete-style knife, according to the complaint. The couple lit the remains on fire and buried them in three separate holes near the Leon River, the complaint said.

Investigators told her to call Specialist Robinson. During the conversation, he denied doing anything to Private Guillen.

But he later texted Ms. Aguilar pictures of news articles about the discovery of human remains near the Leon River.

“Baby they found pieces,” court documents quote him as saying during a phone call with Ms. Aguilar, which investigators were monitoring. “They found pieces.”

Michael Levenson contributed reporting.