The mysterious disappearance of 12 people from a Mexico City after-hours bar nearly two weeks ago was the work of a local gang, authorities said, with the possible motive being a dispute between rival groups over drug dealing.

There has been no word of the 12 since they vanished in broad daylight on May 26 just a block from Mexico City's leafy Paseo de Reforma. City Prosecutor Rodolfo Rios showed a surveillance videotape to reporters late Friday that disputes witness' accounts that the missing were taken by masked commandos with large guns and SUVs.

The videotape shows several compact cars pulling up, and people being herded in just a couple at a time. The men taking them are in civilian clothes, and there are no signs of weapons or force, explaining why so many people could disappear without detection in the middle of a busy Sunday. There was both a mass bike ride and 5-kilometer (3.1 mile) foot race less than a block away when they were seen leaving the bar about 11 a.m.

Rios said the abduction involved at least 17 people in eight vehicles. He said so far authorities can only place eight of the 12 at the after-hours bar known as Heaven, which was located on a small side street in an upscale business district of towering high-rises. Four people have been detained so far in the crime, including an owner of the bar and two employees.

The missing all lived in Tepito, one of Mexico City's most dangerous neighborhood's and home to its largest black market.

Four people were gunned down in a gym late Thursday night in the same neighborhood, raising fears that a wave of cartel-style violence was hitting the city. Two men were detained but later let go, Rios said.

Mexico City authorities spent all day Friday assuring residents that the two crimes were not related and that the incidents are not signs of large-scale drug violence seen in other parts of Mexico.

The crime in the gym, an assassination targeted at two brothers, is not related to the disappearance of the young, he added.

"I don't have any indication of any cartel in Mexico City," Mayor Miguel Angel Mancera told the Televisa television network. "It's not a cartel. What we have in Tepito is an upswing in violence, and an upswing in some gangs."

A witness to the alleged kidnapping told authorities that is was the result of a dispute between two rival groups of drug dealers operating in Tepito, Rios said, but added that it's just one line of investigation.

Tepito is the main clearinghouse for millions of dollars of contraband, from guns and drugs to counterfeit handbags that come through Mexico City.

Mancera said authorities were investigating whether the alleged mass kidnapping might have been related to the execution on May 24 of a low-level drug dealer outside a bar in the trendy Condesa neighborhood. A public security official who was not authorized to be quoted by name had said that the killing of the dealer outside the "Black Bar" was related to the disappearances two days later, and that both may have been part of a turf battle between drug gangs.

"The Heaven bar and the Black bar have some threads in common, which prosecutors are investigating," Mancera said. "These two events could lead us to the conclusion that they are related."

But he said "we have found nothing to connect" the Thursday gym shootings with the bar case.