Three suspected migrants were arrested Monday for allegedly killing a Mexican immigration agent who had asked to see their identification documents, Mexican officials say. 

The migrants — two from Venezuela and one from Colombia — were arrested hours after an alleged attack on the agent, who was found earlier in the day with no signs of life, state security and migration officials said. The attack took place around 30 miles south of the U.S./Mexico border.

State investigators confirmed that the immigration agent suffered a head injury and was found with no vital signs. His body also showed “signs of violence,” according to a statement from public security officials with northern Chihuahua state.

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The agent was identified as Luis Alberto Olivas García, who had worked for the immigration agency for 30 years.

The slain agent was attacked at a checkpoint just south of Ciudad Juarez, which is across the border from the U.S. city of El Paso, Texas, when he asked an unspecified number of foreign nationals for their identification documents, according to the National Migration Institute.

Preliminary reports indicated that the agent had sustained several wounds possibly caused by a sharp weapon and a head injury most likely caused by a rock, the New York Times reported, citing the Chihuahua security ministry, Jorge Armendáriz. 

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Olivas García had been recognized earlier on Monday for his 30 years of service, Armendáriz added.

The death of the agent marked a rare case of deadly violence against agents and comes as migrants try to cross into the U.S. ahead of an impending crackdown on illegal crossings when President-elect Trump is sworn into office. 

Hundreds of U.S.-bound migrants waited in long lines outside an immigration office in southern Mexico on Monday, hoping to secure safe passage north and enter the U.S., according to Reuters.

The U.S. recorded an unprecedented number of illegal migrants flowing across its borders under the Biden-Harris administration.

A cornerstone of Trump’s second term in office is to secure the border and carry out the largest mass deportation program the U.S. has ever seen.

Reuters contributed to this report.