A stabbing at a benefit for an injured motorcyclist at the Boston Teachers Union Hall in August remains unsolved because every person inside the hall interviewed by police either said they saw nothing or refused to talk, a police detective says.

Sgt. Det. Kenneth O'Brien told the Boston Licensing Board on Tuesday that even the victim told police he saw nothing early on Aug. 3, only that "he was walking around the hall when he felt a pop on his left side" and then looked down to see blood. The board held a hearing to determine whether the hall, at 180 Mt. Vernon St., could have done anything to prevent the stabbing.

O'Brien said that when police arrived at the hall shortly after 2 a.m., they saw numerous people in "motorcycle-type groups, wearing their colors."

Hall Manager Michelle Frank said she'd requested two detail officers from BPD for that night but that the positions went unfilled.

The motorcycle group that rented the hall, however, supplied 12 members for security, she said. Frank did not name the group, but said that in addition to that group, two other groups were invited. But she said members of a fourth group showed up as well.

She said that eight or nine hall staffers were also on duty, but that none of them saw the stabbing.

She added that as soon as she learned of the stabbing, she instructed the hall's bartenders to stop serving drinks. She said she kept the music going, however, in the hopes that people would filter out slowly, rather than "dumping everybody into the parking lot."

The board decides Thursday what action, if any, to take against the hall.