More than 200 people were detained for questioning at a nightclub in the northern Mexican city of Monterrey as part of an investigation into this week's slayings of nine individuals, although most were later released, officials said.
Dozens more were still being held at the State Investigations Agency, or AEI, headquarters in Monterrey, all workers at the La Eternidad nightclub where the nine people killed by suspected gang members had been before their deaths and which is suspected of being a drug-distribution point.
"A search was carried out (in the wee hours of Friday morning) at La Eternidad because the eight men and the woman killed (early Thursday) were found to have that club's stamp on their wrists," Nuevo Leon state Security Council spokesman Jorge Domene said.
After closing the facility, authorities detained the 204 people found inside at the time and took them to the state police headquarters.
Of them, Domene said 142 have since been released while 62 others who worked at the club as waiters and waitresses, bouncers and even musicians remained in custody.
Dozens of police and army soldiers took part in the operation at La Eternidad, located in downtown Monterrey.
Authorities are trying to determine if the eight young people and the woman gunned down in the center of that metropolis knew each other and had been sitting together at a table at the nightclub.
Initial reports on the slayings said armed subjects climbed out of several vehicles around 5:00 a.m. Thursday, lined up the eight young men against the wall of a building in downtown Monterrey and opened fire.
The woman was fatally shot nearby in the Paseo de Santa Lucia, a tourist attraction in the center of that metropolis.
Authorities are investigating whether the establishment was a drug-distribution point like the Sabino Gordo nightclub - linked to the Los Zetas gang - where 20 people were killed last July, Domene said.
The attack at Sabino Gordo was attributed to the Gulf cartel, while a message left at the scene of Thursday's massacre has led investigators to suspect Los Zetas were the perpetrators.
A territorial battle between the Gulf and Los Zetas drug cartels and clashes pitting criminals against the security forces claimed some 2,000 lives in Nuevo León last year.
The Mexican government said earlier this month that 12,903 people were killed nationwide in drug-related violence between January and September 2011, an increase of 11 percent from the same period in the prior year.
The drug war death toll stood at 47,515 from December 2006, when President Felipe Calderón took office and militarized the struggle against the country's heavily armed drug mobs, to Sept. 30, 2011.
The murder total has grown every year since Calderón was inaugurated.
Unofficial tallies published in December by independent daily La Jornada put the death toll from Mexico's drug war at more than 50,000.