Mexico City (CNN) -- A gang was involved in the mass disappearance of people at a bar and investigators are looking into whether a dispute with a rival group was a factor, officials said.
The May 26 incident at the Heaven after-hours bar has jolted the capital city, given it took place in daylight on a Sunday morning.
Video footage shows a gang of about 17 people arriving in eight vehicles at the fashionable Zona Rosa district, according to authorities.
It's unclear exactly how many people were taken from the bar. Initial reports indicated 12.
But Mexico City Attorney General Rodolfo Rios said Friday that video showed eight people being taken to cars. Authorities don't know what became of the other four people.
Contrary to reports by relatives of the missing, the gang was not masked or driving SUVs -- hallmarks of an organized squad. Rios said it was not possible to determine from video footage whether they were armed.
All of the missing people came from Tepito, an area of the capital known for the sale of contraband, including guns and drugs.
Two of the missing people are sons of jailed criminal leaders, officials said. They are not among the people taken from the bar, according to Rios.
Investigators also are looking at a possible link between the disappearances and a killing that occurred the same weekend in the nearby Condesa area. Police are examining the possibility of a dispute between rival gangs operating in Tepito.
Mayor Miguel Angel Mancera dismissed suggestions the capital is witnessing a rise in activity involving organized transnational drug cartels.
"In Mexico City, we don't think there is a base for a cartel, unlike in other regions," he told CNN.
"The presence of video surveillance, the presence of the federal police, the presence of the Army and the Navy. It would be very complicated for them to operate in this territory."