One of six suspects charged in the 2001 murder of a 22-year-old “Pit Kid” has pleaded guilty to a reduced charge, and has agreed to testify against her alleged co-conspirators.

Ana White, 21, pleaded guilty to manslaughter and kidnapping in the beating and stabbing death of Io Nachtwey, a homeless woman who, like several of the defendants in her murder, frequented the “Pit” near the Harvard Square T station.

White had initially been charged with first-degree murder. But on February 17, she plead guilty to the lesser charges.

According to Suffolk District Attorney (D.A.) spokesman David Procopio, manslaughter carries a maximum prison sentence of 20 years, and kidnapping has a maximum sentence of life in prison.

But, according to White’s lawyer, Norman Zalkind, White’s plea agreement calls for a 12-year sentence, provided that she testifies against the other five defendants.

“If she honestly testifies, then she will probably get that sentence,” Zalkind said. “But it’s still up to the judge’s discretion.”

White has already served more than three years in prison, he said.

Nachtwey—known as “Rook” to her friends in the “Pit”—was allegedly raped, stabbed multiple times, beaten, and then thrown off a railroad bridge into the Charles River on Nov. 3, 2001. Joggers found her body floating in the Charles near the Boston University Bridge the next day.

Prosecutors have accused White of holding down Nachtwey while the others beat and stabbed her. Police at the time attributed the murder to gang violence.

In 2001, the incident prompted the Cambridge City Council to pass legislation calling for increased law enforcement around the Harvard Square area.

“I am much more interested in the public safety approach to this than any other approach,” former Cambridge Mayor Anthony D. Galluccio told The Crimson in an article published Nov. 20, 2001. “I want our police to very simply clean [the ‘Pit’] up.”

But yesterday Cambridge Police Department spokesman Frank T. Pasquarello said safety in the “Pit” isn’t as much of a concern as it was around the time of Nachtwey’s murder.

“There are people with long hair and nose rings and eye pierce rings; sometimes that feels threatening to some people. But it doesn’t bother some people,” Pasquarello said. “Relatively speaking, Harvard Square is very safe—it really does not appear to be anything over and above what you would normally expect in an area of high visibility with large groups of people that congregate.”

Fellow “Pit” dwellers at the time of Nachtwey’s death said that Nachtwey, a Hawaii native, had moved from Maine to Cambridge the summer before her murder. According to friends, she was homeless, and frequently slept in cemeteries.

Jury selection for her murder trial is expected to begin on March 7.

Procopio said that the prosecution entered into the agreement with White for “strategic and tactical reasons.”

“We expect that it will be a lengthy trial—perhaps three to four weeks long, because there are so many co-defendants,” he said.

—Material from the Associated Press was used in the reporting of this story.

—Staff writer Reed B. Rayman can be reached at rrayman@fas.harvard.edu.