This is pretty outrageous, even if it is a "mistake."

A Mexican police helicopter conducting a law enforcement operation on the border, crossed into US territory and fired on American border agents.

CBS Las Vegas:

Mexican authorities were conducting a drug interdiction operation when the incident happened early Thursday morning on the Tohono O’odham Indian Nation. The Mexican chopper fired at the agents and then flew back into Mexico.

However, Mexican authorities have denied shooting at agents and say they were under attack during a mission to find smugglers on the border.

Tomás Zerón, the director of the Mexican attorney general’s office investigative office, said that Mexican military and federal police who were conducting an operation on a ranch in Altar, Sonora, were shot at by criminals. Mexican authorities never fired any weapons and in fact never crossed into the U.S. side of the border, he said.

Art Del Cueto, Border Patrol Tucson Sector union president, tells KVOA-TV, though, that they called and apologized for the incident.

“The incident occurred after midnight and before 6 a.m. Helicopter flew into the U.S. and fired on two U.S. Border Patrol agents,” Del Cueto said in a statement to KVOA. “The incident occurred west of the San Miguel Gate on the Tohono O’odham Indian Nation. The agents were unharmed. The helicopter went back into Mexico. Mexico then contacted U.S. authorities and apologized for the incident.”

Del Cueto said four agents were in a marked patrol vehicle when they were shot at.

“They could say they didn’t fire at the agents intentionally. But for them to say that they were no shots fired within the United States, toward the United States Border Patrol, is a lie. They got in contact with our managers and apologized for the incident,” Del Cueto said.

If it didn't happen, why apologize for it?

As for why it happened, it could be a mistake. Or, it would not be impossible to believe that the Mexican police were running interference for those drug smugglers they were supposedly after. Police corruption is endemic in Mexico and distracting border agents long enough for the mules to get across the border by firing on them is entirely possible.

Next time, just to be on the safe side, we should shoot back.