It began shortly before 10 on Wednesday night with an accusation that a woman had cut in line while waiting for a bus in Queens. It ended less than an hour and a few miles later with a 15-year-old girl lying mortally wounded on the sidewalk.In between, according to the authorities, a 39-year-old security guard on his way home from work traded unkind words with passengers on the Q85 bus. Officials said that a group of boys followed him off the bus at his stop in Springfield Gardens, where they were joined by several other teenagers, and that the security guard, claiming later that he had been pelted with bricks and bottles and feared for his life, took out a knife and stabbed one of his tormentors, a girl, in the chest.
Others who were with the girl, identified by the police as Keyanna Jones, held down the man, Winston Alladin, the authorities said, until the police arrived. Keyanna was pronounced dead on arrival at Jamaica Hospital Medical Center. She had completed her freshman year at John Adams High School in Far Rockaway earlier that day.
“She was going to that school because she wanted to become a lawyer,” said Dot Jackson, her great-grandmother.
On Thursday, Mr. Alladin was charged with manslaughter and criminal possession of a weapon. He pleaded not guilty at his arraignment shortly before 1 a.m. on Friday, and Judge Robert Raciti of Queens Criminal Court set Mr. Alladin’s bail at $250,000 cash or bond.
Detectives went house to house near where the stabbing took place in Queens, looking for witnesses to the attack.
An assistant district attorney, Mario Karonis, said at the arraignment that Mr. Alladin’s “self-defense claims were taken into account” by prosecutors when they filed the charges.
Mr. Karonis added that “there are multiple witnesses,” not all of whom “necessarily support the statements made by the defendant.”
The authorities identified Mr. Alladin as an immigrant from Trinidad and said that he was on his way home from his job as a security guard at Takashimaya, a luxury Japanese department store on Fifth Avenue in Midtown Manhattan, when his path ultimately crossed Keyanna’s. The police said that he had no prior criminal record.
Inside Takashimaya, the head of security, who identified himself only as Joshua, said of Mr. Alladin: “I’ve known him for the last eight years and this person is not a violent person. He’s a good person. He’s not a person who looks for trouble.”
A relative held up photographs of Keyanna Jones, 15, who was fatally stabbed on Wednesday night in Queens.
Investigators said Mr. Alladin told them that the stabbing arose from an argument he got into with a woman as he and the woman were boarding a city bus at Archer and Jamaica Avenues.
Mr. Alladin said he accused the woman, who had a child in tow, of jumping ahead of him in the line, the authorities said.
The dispute continued on the bus, where, Mr. Alladin said, three boys converged on him and began to harass him for speaking disrespectfully to the woman, Police Commissioner Raymond W. Kelly said.
When the woman got off the bus at her stop, Mr. Alladin and the boys stayed on. The boys continued to taunt Mr. Alladin, the police said he told them.
When Mr. Alladin disembarked in Springfield Gardens, the three boys followed him and were joined by a larger group of youths, including Keyanna. The entire crowd, which numbered at least 10 at this point, trailed Mr. Alladin, he told the police.
Mr. Kelly said that according to Mr. Alladin’s account, Mr. Alladin walked into a nearby backyard and asked the residents for help. “He asks someone to call 911,” Mr. Kelly said. “They actually tell him to get out of the yard.”
Shortly afterward — as the crowd continued to surround him, according to Mr. Alladin’s account — he pulled out a folding knife, which the police said he used to stab Keyanna in the chest.
The police said that the stabbing occurred in front of 137-42 Bedell Street in Springfield Gardens. They arrested Mr. Alladin at 10:34 p.m. They gave his address as 137-46 Bedell Street.
Michael Simpson, 10, with Diane Tigue, his aunt, was present at the start of the dispute and spoke to investigators.
At the arraignment, Mr. Alladin’s lawyer, Stephen Bilkis, said Mr. Alladin told him he was attacked based on some “issues” stemming from the fact that he and his fiancée were the only Trinidadians living in the neighborhood.
Before the stabbing, Mr. Bilkis said “there was name-calling, there was rock throwing.” He added: “My client was calling for help. No one was responding to him.”
The police said late Thursday afternoon that they were still trying to find the woman with whom Mr. Alladin had the initial dispute. They were also tracking down the driver of the bus and the people who had placed calls to 911.
A law enforcement official said that the police had interviewed the three boys who had confronted Mr. Alladin on the bus, and that their accounts differed somewhat from his.
According to the official, Mr. Alladin told investigators that as the crowd of youths was closing in, they pelted him with bottles and bricks, then rammed him with a shopping cart. The police said that some of the calls to 911 corroborated that claim.
But the boys, a law enforcement official said, claimed that the objects were hurled only after Mr. Alladin stabbed Keyanna.
Also, Mr. Alladin said that he was merely holding his knife in front of him and swinging it back and forth as an attempt to hold the crowd at bay, but some of the youths who spoke to investigators told them that he was the aggressor, the law enforcement official said.
Detectives in Springfield Gardens, Queens, asked residents if they saw the stabbing of Keyanna Jones on Wednesday.
Mr. Karonis, the prosecutor, said that Mr. Alladin “told detectives he ‘pulled a knife from his gym bag and swung it at the crowd, and the girl got cut.’ ”
Mr. Kelly described the victim’s wound as a “direct entry into the chest.”
One of the three boys, Ronald Wilson, 15, said on Thursday outside the 113th Precinct headquarters that Mr. Alladin had used racial epithets against the woman on the bus. Mr. Wilson, a cousin, Michael Simpson, 10, and a third boy had been interviewed at the precinct station.
But Mr. Kelly said the police did not believe that racial bias was a factor in the case. “Mr. Alladin is from Trinidad and the three initial assailants, as described by him, are American blacks,” he said. “I have no information as to the language that was used and whether or not there were racial epithets used.”
Outside Keyanna’s house on 183rd Street, a few blocks from the stabbing, her great-grandmother, Ms. Jackson, sat with dozens of the girl’s friends and relatives. Her lips trembled as she said, “She was a good girl, a sweet girl. I loved her and he stabbed her in the heart.”
