A fire that broke out in a Mexican immigration detention center near the border on Monday is now being investigated as a homicide case. The fire killed at least 39 people.

The reason authorities are now considering the incident a homicide case is because upon initial investigations into the cause of the fire, authorities have identified that “government workers and private security employees had not allowed detainees to escape from the blaze,” The New York Times reported.

A video from a security camera inside the facility shows two people dressed as guards who approach a metal gate on the outside of the facility. Per The Associated Press, “At least one migrant appears by the metal gate on the other side. But the guards did not appear to make any effort to open the cell doors and instead ran away as billowing clouds of smoke filled the structure within seconds.”

At least 28 people were injured from the fire in Ciudad Juarez, Mexico, just south of El Paso, Texas.

Authorities believe the fire was started when “a group of migrants gathered mattresses and set them ablaze,” Sara Irene Herrerías Guerra, head of the Specialized Prosecutor for Human Rights of the Attorney General of Mexico, told CNN.

Initial reports claim that some of the dissidents set fire to mattresses that turned out to be highly flammable, causing the fire to spread quickly, NBC News reported.

At least one of the arrest warrants is for one of the people inside the facility who started the fire, as well as for “two federal agents, one state migration agent and several members of a private security company,” according to CNN.

The people killed in the fire were men from Central and South America, AP reported.

Per The Washington Post, some of the 68 residents who were living in the center are likely from Venezuela.

But the National Migration Institute has started “communicating ‘with consular authorities from different countries’ in order to identify the dead,” The New York Times reported.

“With deep sadness and sorrow, we learned about the fire that happened inside the INM of Ciudad Juarez,” Mexican lawmaker Andrea Chávez said in a statement on Facebook. “We will wait for the official information and, from this moment, we convey our condolences to the families of the migrants.”

In February, President Joe Biden’s administration announced a rule that requires migrants to apply for asylum in the countries they travel through to get to the U.S. before attempting to get asylum in the U.S., per CNN.

This story has been updated with new developments.