The shooting took place as the officers were responding to a domestic disturbance call at a home and came under fire.
"What I'm trying to tell you is the officers never had a chance to suspect a deadly assault on them," McAllen Police Chief Victor Rodriguez said at a press conference.
Officers Edelmiro Garza, 45, and Ismael Chavez, 39, were both killed. Garza had been on the force for about nine years, while Chavez had been employed by McAllen for about 2 1/2 years.
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Both officers were pronounced dead at a local hospital.
The suspect, identified as Aldon Caramillo, 23, had a history of arrests. His previous charges included driving under the influence, fleeing from officers, assault and marijuana possession, Rodriguez said.
"These are difficult moments, Rodriguez said. "The officers came here to maintain peace. Instead, they were taken down by gunfire."
"The next few days for us will be very, very difficult," he added.
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McAllen is located in southernmost Texas, along the Mexican border.
"I cannot tell you how many calls I've taken, or missed, in the last couple hours," Rodriguez said. Gov. Greg Abbott sent his prayers to the officers and their families in a call, Rodriguez said.
The officers were not wearing body cameras and Rodriguez said he does not believe the dash camera in the officers' car would have picked up the shooting as it was parked away from the home.
Rodriguez said there was still much they did not know about the incident and the investigation will continue.
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"Our department and our officers stand by each other. Together we're strong and I think that's what will help us through these next few weeks," Rodriguez said.
The officers first met with two people who reported assaults that took place inside a nearby home on the south side of McAllen around 3:30 p.m. Saturday, Rodriguez said.
Rodriguez said the attack happened suddenly and fellow police officers didn't learn of the officers' deaths until arriving to the area moments later.
Camarillo shot and killed himself shortly after opening fire on the officers, Rodriguez said, adding that the suspect hid behind a vehicle after other officers responded to the scene.
Law enforcement from several cities in Hidalgo County gathered Saturday evening at McAllen Medical to honor Garza and Chavez. More than 50 police cars were part of a procession that accompanied the bodies of the officers, who were taken to Hidalgo County pathology for an autopsy.
ABC News and The Associated Press contributed to this report.