Mexican investigators continue to look for clues after a gang rammed several vehicles into a prison and escaped with nine inmates on Wednesday, in one of the most dramatic breakouts the country has seen in recent years.
Authorities in the state of Hidalgo, just north of Mexico City, said in a statement that the pre-dawn attack resulted in injuries to two police officers.
"It was gunfire that lasted for almost an hour," revealed Tula resident Sergio Mesa, who was woken by the sound of explosions around 4 am.
The state's interior secretary, Simón Vargas, said "an armed group burst into the prison aboard several vehicles, and it is worth noting that near the prison, two vehicles were burned as part of the criminal group's operation, as a distraction."
Local media reported that burned-out cars found in the city of Tula after the attack were car bombs.
Authorities said they were investigating how the vehicles caught fire.
However, the condition of the two vehicles - automotive parts were blown dozens of yards away, and the floor of one car appeared to have been punched through by a blast - suggested that it was more than merely a fire.
The use of car bombs by gangs in Mexico has been extremely rare, with one such attack in the northern border city of Ciudad Juarez in 2010 killing three people.
But gangs in Mexico frequently do torch vehicles to distract the police, and vehicles set alight can explode once the flames reach their gas tanks.
The state police said soldiers, police, and National Guard troops had fanned out looking for the escaped inmates.
Police did not identify the armed gang involved in the prison break but suggested one maybe a gang leader.
The incident is one of the most dramatic breakouts the country has seen in recent years with authorities confirming the escapees were all in prison for having committed serious crimes including homicide and kidnapping.
Tula is home to a large oil refinery and the area has been plagued by gangs of thieves who drill illegal taps into government-owned pipelines to extract gasoline and diesel.