“We were despised,” said Ms. Dawydiak, who gave the New Year’s Eve party for her 19-year-old daughter, Rose. “I hate to say it, but I kind of think that had an effect.”  Sgt. Neville Gittens, a police spokesman, dismissed that accusation.  “We don’t show up to a scene and gauge our investigation as to who a person is,” Sergeant Gittens said. “That’s not how we do business.”  He also said that it was too early in the investigation to determine whether the attack could be characterized as a hate crime, in light of the anti-gay slurs during the attack.  Sergeant Gittens defended the department’s initial response, saying that when officers arrived at the scene, a group of young men pointed out four potential suspects but then left before they themselves could be interviewed.  “People stand around and say ‘those are the guys’ and then leave,” he said. “If people don’t stick around, you can’t make an arrest.”  Sergeant Gittens said the chaotic scene after the fight had also complicated the investigation. There may have also been some underage drinking. Ms. Dawydiak, who was not at the party at the time of the attack, said that she and her husband hid all the alcohol in the house before the party, but that some uninvited guests — those believed to have started the fight — might have brought beer.  Whitney Leigh, a lawyer for two of the victims, said that at least two Yale students identified their assailants the night of the attack. “The police had enough information to arrest multiple individuals at the scene,” Mr. Leigh said.  On Tuesday, investigators met with representatives of the San Francisco district attorney, who told the police that more evidence was needed before charges could be filed, a development that the police say is routine.  “Everyone needs to be patient and let us do what we do,” Sergeant Gittens said. “Things take time.”  Still, reports of the attack — and the pace of the police investigation — have buffeted the department, which has weathered several scandals in recent years, including Fajitagate, a 2002 incident involving three off-duty officers who were accused of accosting two men and using excessive force as they demanded that the men surrender a bag of fajitas.  The fajita scandal led to grand jury indictments, lawsuits and a turnover of the top command, even though the three officers initially accused in the attacks were acquitted of criminal charges.  In 2005, the department also endured accusations of prejudice after homemade videos surfaced featuring uniformed and plainclothes officers in racially and sexually charged skits. The videos, made for a department Christmas party, led to an announcement on Nov. 30 by Chief Heather Fong that 35 officers would face disciplinary charges in front of the police commission and the police chief.  In the Yale case, the Aziz family has been particularly vocal, with Ms. Aziz and her son appearing on the Fox News Channel last week with Sean Hannity, the conservative talk show host. Mr. Hannity offered a $10,000 reward for information in the case, calling the Baker’s Dozen “the national anthem singers” because the group had sung “The Star-Spangled Banner” at the party before being attacked.  On Friday, Ms. Aziz said the family was encouraged that the police were making the trip to interview her son, who has since returned to Yale, though with his jaw wired shut for the next five weeks. She said her son had not been cowed by the attack. “He’s absolutely going back to everything he did before,” Ms. Aziz said. “And he’s still going to rehearsals with the group.”  A version of this article appears in print on , on Page A9 of the New York edition with the headline: San Francisco Police Are Criticized in Wake of Fight Involving a Yale Singing Group. Order Reprints| Today's Paper|Subscribe
The investigation stems from an attack just after midnight on Jan. 1, when several members of an all-male a cappella group from Yale were set upon by a group of young men.