CAMBRIDGE, Mass. – For years, Harvard Square has been a place for kids to congregate with friends, to fit in when they might elsewhere be considered misfits, to sleep when they might not have a home.

Io Nachtwey was drawn to this gathering spot, a sunken plaza known locally as “the pit,” adjacent to the subway stop and across from the red brick buildings of the nation’s oldest university. Plain and petite, Nachtwey still felt comfortable among the multicolored hair, tattoos and body piercings.

It was in Harvard Square that Nachtwey met other vulnerable youths who would become her friends. It was also where police say she met her killers.

Nachtwey’s body was found in the nearby Charles River on Nov. 4, the day after prosecutors say she was stabbed to death because she and her friends refused to join a gang.

“She was one of the most innocent people here,” said Josh Mason, 17, from inside the Harvard Square subway station below the pit. “It’s so cruel that she was the one who got murdered. She was a real sweetheart.”

The attraction of Harvard Square is both practical and philosophical. While Cambridge is a liberal bastion, accepting kids who often don’t fit in elsewhere, it’s also a major hub of public transportation.

The subway and several bus lines bring tens of thousands of passengers to the square every day.

It also makes it a popular place to prey on the vulnerable.

Nachtwey, 22, landed here this summer after dropping out of Maui Community College and traveling to the East Coast to stay with grandparents in Maine, friends said.

She would panhandle outside shops at the square, always with a smile.

Just a few years ago, Nachtwey had been named the best female dancer in her senior year at Kekaulike High School in Hawaii, and she’d often give an impromptu dance in the square, friends said.

At night, when many of the other kids go home, Nachtwey would curl up to sleep with other homeless in a Harvard Square cemetery.

Authorities say two of the six people charged with Nachtwey’s death were looking to start a gang with some of the youth who frequented the square. Brothers Luis Vasquez, 19, and Ismael Vasquez, 23, were members of the Latin Kings gang in Lawrence who left that city 30 miles north of Boston two years ago when police cracked down on gang activity, Lawrence Police Capt. Mike Molchan said.

The brothers, along with their friend, 27-year-old Harold Parker, tried to recruit more than a dozen youths; for initiation, they would have to steal and bring the loot to the brothers and Parker, prosecutors said.

When Nachtwey and others backed out, prosecutors say the men decided to kill her to send the others a message.

The Vasquez brothers, Parker and three others led Nachtwey to railroad tracks under the Boston University Bridge. They stabbed her 15 times with knives, beat her with martial arts weapons and rolled her body into the Charles River below, according to police.

The brothers, Parker and Scott Davenport, 27, of Cambridge, are being held without bail on murder charges. Ana White, 18, of the upscale suburb of Milton, and Lauren Alleyne, 18, a former cheerleader at Malden High School, are charged with being accessories before the fact. Police say the young women pushed Nachtwey onto the tracks while the others stabbed her.

Jonathan Shapiro, an attorney for Parker, said prosecutors are trying to win the case in the media before they have concrete evidence.

“It’s too soon for any of the forensic tests to be done,” he said of weapons found by police. “The only things he could base his case on are statements from a group of very unreliable witnesses, no two of whom probably gave the same story.”

A friend of Nachtwey, who identified herself only as “Daher,” said the four men charged with murder sometimes hung out in the pit. But she says there was no gang recruiting.

Peter Parker, attorney for the Vasquez brothers, and Alleyne’s lawyer did not return calls to comment. Home numbers for Alleyne and White are not published.

Bill Sugane, a foreign language teacher at Nachtwey’s high school, remembered Nachtwey as an average student, but outgoing and self-assured. She came from a family with strict rules.

In Hawaii where skirts and shorts are common, she and her sister were not allowed by their parents to wear clothes that revealed their legs, Sugane said.

“They were very strict with her,” he said. “Her mother always had her head covered, but not in an Arab way.”

Sugane said the Nachtweys were not from Hawaii, but he did not know their native state nor where they currently live. A message left for a number once registered in Hawaii to Io’s father, Floyd Nachtwey, was not immediately returned.

Sugane said he did not recall Io complaining about her parent’s strict rules.

“They preached self-reliance,” he said, noting that Io, named after a moon of Jupiter, worked part-time at the local public library.

“She was always the first one in class and the last one out,” said Sugane, adding that she tried to learn French, Spanish and German at the same time. “I told her, ‘You really need to focus on one.’ She was very passionate about anything she did. She had no inhibitions at all.”

Nachtwey’s death was the latest tragedy for pit kids.

In 1999, a man was charged with drugging and raping teen-age boys he met in the pit.

He used pharmaceutical-grade morphine, prescribed because he had AIDS, to knock out his victims, police said. He died before his trial.

In 1997, a then-16-year-old runaway from Maine told police she was raped by a Boston man who befriended her in the pit and shared his drugs with her. A man who was free on personal recognizance for a separate rape charge was acquitted in the assault.

“What makes them more vulnerable is that they’re looking to belong,” said Genny Price, associate director of Bridge Over Troubled Waters, a youth outreach group. “That’s one of the real attractions of Harvard Square, you can fit in. They’re looking for love, to feel cared about, and to be connected.”