CARTAGENA, Colombia — In the early hours of April 12, the booze flowed and a thumping techno rumba shook the walls at Tu Candela, a popular nightclub whose dance floor recalls the narrow confines of a wine cellar.

Dozens of couples gyrated to the pulsing sounds emanating from flat video screens throughout the club, which is in Cartagena’s walled-in colonial section. When the party ended around 4 a.m., two couples headed for the Hotel Caribe, an imposing castle-like structure facing the Caribbean, two miles from the club.

The couples’ encounter at one of Cartagena’s hottest nightspots set the stage for the still-unfolding prostitution scandal that’s snared 12 U.S. Secret Service agents and a dozen members of the U.S. armed forces.

The military personnel remain under investigation. Of the Secret Service agents, eight have resigned, retired or been fired and one has had his national security clearance revoked, making his dismissal almost certain. Three have been cleared of misconduct.

But the investigation is hardly over; the scandal has added a new issue to the presidential campaign and raised questions in Congress about whether contact with prostitutes by members of the advance team preparing for President Barack Obama’s attendance at the April 14-15 Summit of the Americas compromised Obama’s security.

U.S. investigators who’ve traveled to Cartagena to interview hotel chambermaids as well as taxi drivers who transported the women and the Secret Service are still trying to unravel events, according to hotel employees and drivers. One driver said that as recently as Monday a man who identified himself as a U.S. investigator had approached him with pictures of women who might have slept with agents at the Caribe.

Whether investigators have requested hotel video and copies of identification cards the women presented at the reception desk isn’t known. Ana Beatriz Angel, a Caribe spokeswoman, declined to discuss the matter. “The hotel will make no comment,” she said.

The Associated Press reported Wednesday that the Secret Service acknowledges it’s checking whether its employees consorted with strippers and prostitutes in advance of Obama’s visit last year to El Salvador.

The Colombia scandal erupted when Dania Suarez, 24, who was one of the two women dancing at Tu Candela, began knocking on hotel room doors, complaining that her date had refused to pay after having sex with her.

Suarez and the second woman, still unidentified, left the Caribe between 9:30 and 10 a.m. They were escorted to a nearby taxi stand by police officers who had responded to the ruckus in the hotel hallway.

Once they got into the taxi, Suarez and her girlfriend talked about their misadventure.

Suarez’s friend was puzzled that her date had declined to have sex with her.

“Aren’t I pretty?” she asked the cab driver, Jose Pena, as he drove away from the Caribe on Cartagena’s busy seaside highway.

Suarez recalled that her date was a cheapskate. He’d promised to pay $250 for sex but had given her only about $30. After she complained in the hallway, men in other rooms pitched in and gave her $100.

In her first interview in The New York Times last week, Suarez was quoted as saying that the promised amount was $800. She hasn’t denied that statement, but Pena said she didn’t mention that figure in his presence.

While fallout from the scandal has engulfed Pena, Suarez and U.S. security personnel, little has emerged about how all the agents and military men in question came to meet the women. Encounters with more than 20 women have been rumored, but not confirmed.

Precisely how many security people were dispatched to Cartagena to advance Obama’s visit is also unknown.

The Secret Service and other agencies, including the Pentagon, typically deploy hundreds of agents and support personnel to check hotels where the president will stay, buildings he’ll visit and roads on which he’ll travel.

Employees at the Caribe said they remembered perhaps up to 30 agents who arrived eight to 10 days before the summit.

“They would sit in groups of three or four at the breakfast room, or would lounge by the pool or exercise at the gym,” said one worker, who like others didn’t want his name printed for fear of losing his job.

Drivers at the hotel taxi stand remembered some of the agents walking two dogs on the hotel grounds. Other drivers recalled transporting some of the agents to supermarkets to buy bottles of water and juice. One of their favorite supermarkets was Carulla, which resembles organic food outlets such as Whole Foods.

The agents were mostly white men, but drivers saw at least one woman with short blond hair and a few Hispanic and black men. Most wore shorts and sport shirts.

Nearly every day the agents left the hotel in the morning in groups of three or four to walk along the coastal road that Obama would travel on arrival and the next day to the summit at the Convention Center near the colonial section.

On one occasion, one driver said, three agents asked him to take them to the corner of Ricaurte and San Juan de Dios streets in the colonial section. There, they met three other agents and some Colombian police officers who were lowering a camera through a sewer manhole on the sidewalk.

The location was one block from San Pedro Claver Plaza, where Obama attended an event hosted by Colombian singer Shakira.

An early hint of the brewing storm came four days after the agents arrived, several taxi drivers said.

“I remember seeing some of them talking to or walking with young women in front of the hotel or near the hotel along the seaside road,” one of the drivers said.

None of them said they saw women enter the hotel with agents. Also, none said they saw agents drinking.

What agents did at the end of the workday is unclear, but many foreign visitors gravitate to restaurants and bars in the colonial section, where buildings are elegantly lit at night. Tu Candela is one of the major spots there along with the Cafe Havana, where Secretary of State Hillary Clinton was spotted dancing during the summit.

Young Colombian women also flock to the area — many to eat, drink, dance or to find dates, and some to sell sex.

Pena recalled that Suarez didn’t speak English, but that her friend did and assisted with translation during the non-payment incident at the hotel.

El Tiempo said the women and their Secret Service dates, whose names haven’t been revealed, took a cab from Tu Candela to the Caribe in the early hours of April 12. Suarez and her friend provided their identification cards at the hotel’s reception desk. Then the couples went to separate rooms.

While only Suarez and her friend have been connected to two agents, U.S. officials have indicated that more than 20 prostitutes may have been involved with agents and military personnel. Details of those encounters have yet to emerge.

©2012 the McClatchy Washington Bureau