One night a month, police say, the inside of the modest Mummers' Downtowners Fancy Brigade clubhouse in South Philadelphia transformed into a bacchanalian free-for-all where dozens of men ate, drank, and had sex with prostitutes in full view of each other.

For a $30 cover charge, attendees got one free beer from the cash bar, food, and access to the women at the party. The women, police said, walked around scantily clad or naked, charging from $30 to $100 for sex.

On Tuesday night, the festivities came to an abrupt end when police officers swarmed the two-story building near Second Street and Snyder Avenue. About 50 men and 20 women were inside.

Police arrested 13 people in the prostitution sweep, including 10 women and two executives of the Downtowners.

John Murray, 56, of Deptford, the club's financial secretary, and Alfred Sanborn, 44, of South Philadelphia, its steward, were arrested on liquor violation charges. The two acted as bartenders during the parties, and the clubhouse did not have a liquor license, police said.

Lawrence Crovetti, 65, of Feasterville, was charged with promoting prostitution by arranging for the women to get to the building. Police said he organized the parties and rented the building each month. Authorities on Wednesday were uncertain how long the parties had been held at the clubhouse.

Calls to multiple members of the Downtowners were not returned Wednesday.

The Philadelphia New Year's Shooters and Mummers Association said in a statement that the events at the club had taken place without the knowledge or approval of the association, and that any money raised that was found to be linked to illegal activities would be donated to charity.

Murray and Sanborn were aware of the prostitution, said Deputy Police Commissioner William Blackburn, but police did not have enough evidence to charge them with prostitution-related offenses. The dozens of men seen interacting with the women were not arrested, either.

"We weren't privy to the conversations between the males and the females, where there was a price and a particular act that was identified," Blackburn said. "Our main targets were the females."

Police also seized about $4,000 from the clubhouse, as well as a handgun, the owner's permit to carry, and a small amount of drugs.

Police said they did not know whether the money collected at the parties was for Mummers-related expenses.

The Downtowners group, which was formed in 1959, is among the most successful Fancy Brigades. Its website advertises its clubhouse as available for rental for parties, citing its air-conditioned banquet hall, full kitchen facilities, and "clean, modern bathrooms."

The investigation into the club began almost two months ago, after police received tips that women were soliciting sex on the second floor of the building every second Tuesday of the month between 7 and 11 p.m., Blackburn said.

Lt. Charles Green of the citywide vice unit said an undercover officer gained access to one of the parties last month after wrangling an invitation from Crovetti. Inside, the officer saw women walking around wearing next to nothing, as well as about 50 men.

About 7:30 Tuesday night, two undercover officers made a repeat visit to the party. As the officers made their way around the building, they saw a man pulling his pants up near a naked woman in one room, and others engaging in sex acts in view of the bartenders and others. Meanwhile, Green said, 10 women approached the officers about paying for sex.

"It was just so out in the open, and so obvious what was going on," Green said.

Neighbors of the clubhouse appeared shocked by the news, and some expressed disgust at learning that the parties were occurring in what they considered a family-oriented neighborhood. However, many declined to give their names and said they feared retaliation from club members if they criticized the group.

One woman said that most club members live in New Jersey or Delaware, and that she always knew they when they were having a party by the cars with out-of-state license plates parked on the street.

"It's shocking to all of us," she said. "This is not the kind of neighborhood where you expect something like this to happen."

Another neighbor, whose grandfather was a Mummer, lamented the damage to the organization's reputation.

"I think it's a disgrace," he said. "There are young kids who want to take the time to learn about the traditions of the Mummers, and sew the costumes, and they destroyed that sense of heritage."

Some neighbors said they had heard of exotic dancers being hired for poker games at the clubhouse.

"I heard they had strippers with their card games," said Jimmy Fiocca Jr. "But it was by invitation only. And I never thought they were prostitutes. No one thought that."

Also arrested were Philadelphia residents Michelle Lauber, 32; Sherry Davidson, 40; Regina Mahoney, 26; Chiante Galezniak, 35; Adriana Arena, 51; and Alexis Simon, 24. Police also arrested Virginia Ruiz, 46, of Bear, Del.; Judith Jacobs, 36, of Sicklerville; Jennifer Quenderfield, 36, of Conshohocken; and Barbara Gogos, 44, of Cheltenham.

Police describe the scene Tuesday night inside the Downtowners Fancy Brigade clubhouse at