BBC News
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image captionMost of the victims are believed to be from Comitancillo, where relatives have been given DNA tests
Twelve police officers have been arrested in the northern Mexico for their alleged connection to the killing of a group of migrants last month.
The bodies of 19 people were found in a burnt-out vehicle near the US border in Tamaulipas state on 22 January.
Most of the victims are believed to have been Central American migrants.
Investigators think they were killed as part of a turf war between criminal gangs over control of migrant smuggling routes in the area.