A preliminary investigation has concluded that a 13-year-old Blacksburg girl was stabbed to death and that she probably died on Jan. 27, the day she disappeared from her home, a prosecutor said at a Tuesday news conference.

Mary Pettitt, commonwealth’s attorney in Montgomery County, Va., also announced an additional count against one of the two Virginia Tech students charged in connection with the abduction and slaying of Nicole Lovell.

Natalie Keepers, 19, of Laurel, Md., now faces a charge of accessory before the fact to first-degree murder, meaning authorities allege that she played a role in the events leading to Lovell’s killing. She had previously been charged with concealing Lovell’s body and a misdemeanor accessory-after-the-fact count. The new charge carries a much stiffer maximum sentence upon conviction: life in prison.

Another freshman, David Eisenhauer, 18, of Columbia, Md., is charged with abducting and killing Lovell. Lovell’s family has said it was told that Lovell and Eisenhauer met online, but authorities have not detailed the nature of their relationship.

Nicole Lovell, when she was 10, in Blacksburg, Va. The 13-year-old girl was found dead just across the state line in Surry County, N.C., and two Virginia Tech students are charged in the case. (Tammy Weeks/AP)

Tammy Weeks, Lovell’s mother, also spoke at the news conference, clutching a stuffed panda bear to her chest. She spoke in hushed tones about her daughter’s health struggles and love of pandas but grew so emotional that she was forced to stop.

Josh Blankenship, Lovell’s youth pastor, finished the statement: “Our hearts still ache in sadness.”

Blacksburg’s police chief, Anthony Wilson, said authorities had received around 400 tips from the public about the case. Police said Tuesday evening that a funeral for Lovell was scheduled for Thursday in Blacksburg.

The news conference provided a few new details, but it left many basic questions about the case unanswered. Authorities took no questions from the media.

Police have not said what happened to Lovell after she disappeared from her home or revealed a motive for the slaying.

Weeks spoke at length about her daughter, whom she called “Coley.” Lovell had a liver transplant as an infant and “fought for her life,” coming home from the hospital after her first birthday.

“She tried to live a normal life,” Weeks said. But then Weeks said Lovell was diagnosed with non-Hodgkin’s lymphoma and spent six months in a coma after developing acute respiratory distress syndrome.

Two Virginia Tech students are charged in the death of a seventh grade girl. Here is what you need to know about the investigation. (Claritza Jimenez/The Washington Post)

“At this point, we almost lost her for the second time,” Weeks said.

Medical experts and physicians told Weeks that her daughter had a 1 percent chance of survival, but Weeks said, “Coley once again beat the odds.”

Lovell loved pandas, music and dancing and dreamed of being on “American Idol.”

As she spoke, Weeks began to tremble. She placed her hand to her chest.

“Nicole touched many people through her short life,” Weeks said before walking away from the podium, close to sobbing. “I can’t do it.”

Lovell went missing after she pushed a nightstand against her bedroom door and apparently climbed out a window that was found open, her mother said. Her body was discovered Saturday afternoon near the Virginia-North Carolina border.

Weeks previously said that her daughter needed to take daily medication for her liver transplant and that she had been bullied at school. Police have not said whether either of those issues played a role in her death.

Eisenhauer was arrested early Saturday at his dorm at Virginia Tech and was charged with abduction and first-degree murder. On Sunday, police arrested Keepers and charged her with felony counts related to helping dispose of Lovell’s body. Both were engineering students.

An arrest warrant, revealed Monday, included a brief statement that Eisenhauer had given to authorities: “I believe the truth can set me free.”

Pettitt did not say what prompted authorities to file the new charge against Keepers, but an arrest warrant states that the action occurred between Jan. 4 and Jan. 27.

At the court hearing Monday, a judge set March 28 preliminary hearings for both defendants. Neither has entered a plea yet, and attorneys for both declined to comment Tuesday. Pettitt said the final results of Lovell’s autopsy won’t be ready until just before the hearing.

In the meantime, Blacksburg area residents were sharing their memories of Lovell.

Jane Lillian Vance once taught at Virginia Tech, where she met a student in her class named Morgan Harrington. In 2009, Harrington disappeared during a ­Metallica concert in Charlottesville. She was missing for more than 100 days; her body was eventually discovered in a field.

Vance was inspired by Morgan’s life to join the national nonprofit Help Save the Next Girl, founded by Harrington’s parents, to advocate for young women who have gone missing.

Now Vance has been touched once again by the disappearance and death of one of her students. As an instructional assistant at Blacksburg Middle School, Vance was acquainted with Lovell, a seventh-grader.

“Nicole was a very cheerful and innocent 13-year-old who was full of kindness and wept at cruelty,” Vance said. “She was a good-hearted little girl.”

Vance said that she saw Lovell in the hallways. In a column she wrote in the Virginia Tech student newspaper, Vance described her as “a little mountain angel,” who wore pink and brown cowgirl boots but now will never outgrow them.

Vance said in an interview that she saw Nicole as a “child” and said that depictions of her as a “teenager” made the seventh-grader seem older than her years.

“I prefer to call her a child because her heart was innocent,” Vance said.

Vance wrote that Lovell’s life was “abbreviated” and ended by a predator. “Her obituary is brief, isn’t it?” Vance wrote in her column. “Cut, like a ribbon.”

DeNeen L. Brown and Laura Vozzella contributed to this report.