Police investigating reports that American swimmer Ryan Lochte and three of his teammates were robbed at gunpoint in a taxi so far have found no evidence supporting the account, and say the swimmers were unable to provide key details in police interviews.

A police official with knowledge of the investigation told the Associated Press on Tuesday police cannot find their taxi driver or witnesses. The official spoke on condition of anonymity because the investigation is ongoing.

Lochte’s attorney, Jeff Ostrow, said there was no question the robbery happened and that Lochte had 24-hour security hired after the incident. He hasn’t been leaving his hotel room since.

‘‘This happened the way he described it,’’ Ostrow said.

According to Lochte and the United States Olympic Committee, the swimmers were returning to the athletes’ village by taxi after a night out at the French Olympic team’s hospitality house in the Rodrigo de Freitas area in the upscale south zone of the city. The outing was several hours after Olympic swimming ended Saturday night at the Rio Games.

Traveling with Lochte were Gunnar Bentz, Jack Conger and Jimmy Feigen.

The group did not call police, authorities said, and officers began investigating once they saw media reports in which Lochte’s mother spoke about the robbery.

Lochte signed a statement on Monday confirming the facts he provided, his attorney said.

Russia docked

Russia was stripped of a relay gold medal from the 2008 Beijing Olympics after one of its female runners tested positive for steroids in a reanalysis of her doping samples.

Sprinter Yulia Chermoshanskaya tested positive for two drugs — stanozolol and turinabol — and has been retroactively disqualified and stripped of the gold in the women’s 4 x 100-meter relay, along with her teammates, the IOC said.

Chermoshanskaya was also disqualified from the 200, in which she finished eighth.

Belgium stands to be upgraded to the relay gold, with Nigeria moving up to silver and Brazil to bronze.

Dropping the ball

Rio Games organizers dropped the ball at the start of the Games in terms of logistics and other details.

Games spokesman Mario Andrada said senior IOC officials complained that transportation logistics were not as good they should have been.

Andrada said: ‘‘You need to provide good service and we were kind of dropping the ball a little bit in the beginning,’’

Games organizers made adjustments including having professional instead of volunteer drivers transport IOC guests at the Olympics.

US women beached

The American duo of Kerri Walsh Jennings and April Ross lost to reigning world champs Agatha and Barbara of Brazil, 2-0, in women’s beach volleyball, ending their quest for Olympic gold.

It was the 38-year-old Walsh Jennings’s first lost in Olympic play. She has won three gold medals.

The Americans will play Germany on Wednesday for the bronze.

Step closer

Karch Kiraly’s top-ranked US women’s team moved one step closer to its goal of capturing the Americans’ first volleyball gold, defeating familiar opponent Japan in straight sets to reach the semifinals in Rio.

The unbeaten US won, 25-16, 25-23, 25-22, and has dropped just five sets all tournament. It has faced Japan more times than any other team since 1983. The Americans have won the last three meetings on the Olympic stage against Japan, opening the 2008 Beijing Games with a four-set victory after sweeping Japan in 1996.

The Olympic channel

On Sunday night, right after the flame has been extinguished, another Olympic project will burst out of the starting blocks.

It’s the launch of the Olympic Channel, a $450 million venture designed to keep Olympic sports and athletes relevant in the years between each games and attract new, younger audiences.

The digital channel, which will operate 24 hours a day, 365 days a year, will go live after the closing ceremony of the Rio Games.