It is unclear how many of the missing were kidnapped or killed by drug gangs, which frequently bury their victims in clandestine graves. While President Enrique Pena Nieto has said drug violence has declined, the number of new missing persons reports during the first two years of his administration has remained steadily high.
Interior Secretary Miguel Angel Osorio Chong said Thursday a total of about 28,000 missing-persons reports had been filed between 2006 and 2012, under the previous administration of president Felipe Calderon.
Osorio Chong said about 14,700 of the missing from the previous administration have been found alive and about 750 confirmed dead. Many who had filed missing persons reports didn't update them when their relative re-appeared, he said.
"The young woman who left, eloped with her boyfriend, or the person went elsewhere to find work, and I'm not just saying the United States, they might have gone to another (Mexican) state," Osorio Chong said in a report to congress. "Or there's a marital conflict, and when the person leaves home, they go and file a missing person report."
"But when this youth returns, this migrant returns, this person who had a family problem, nobody goes to report, 'I found my relative,'" he told congressmen.
About another 3,000 people were reported missing in 2013 and early 2014, under President Enrique Pena Nieto's administration, boosting the outstanding total to 16,000. About 8,000 people have been found alive and about 400 confirmed dead since then, yielding the current running total of about 8,000.
Osorio Chong's initial report was unclear about whether the 8,000 were in addition to the 13,000 still missing from the previous administration. But his department later said the 8,000 figure was the current tally for both administrations.
"Talking about whether there were 20,000 or 40,000, the truth is, it is not even possible to say many people there were" who disappeared, Gallo said. While authorities have begun taking DNA samples from victims buried in clandestine graves, Gallo said it is not even clear whether authorities in Calderon's administration investigated all reports of suspected mass graves.
Security analyst Alejandro Hope said that releasing the early, higher number - a top estimate quoted at the time as 26,000 missing - was a "major error," because the numbers had not been reviewed to see if people had been found. "What had been presented as a gigantic humanitarian crisis, is now being revealed is certainly a problem, but is a problem of a different order of magnitude," Hope said.
Still, nobody is declaring victory in the drug-fueled conflicts that have left at least 70,000 confirmed dead in Mexico since 2006.
Hope noted that, despite the drop of 15.4 percent in homicides between 2012 and 2013, Hope noted "the numbers are still abysmal."
He predicted an official full-year tally of homicides in Mexico in 2013 which is to be released soon would show about 23,000, "is equivalent to all of the homicides in Europe in a year."
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