MEXICO CITY -- The Mexican Attorney General’s Office on Friday charged 14 federal police officers with first-degree attempted murder in the Aug. 24 ambush of a U.S. Embassy vehicle and offered new details that make it clear the police were on a mission of slaughter when they opened fire on the vehicle on a mountain road outside the Mexican capital.

In revealing the charges, the Attorney General’s Office said the officers had fired 152 rounds from assault weapons at the black Embassy Toyota SUV. The armored vehicle largely held up under the assault, but two Americans, reportedly CIA officers, were wounded. A Mexican naval captain who was riding in the back seat was unhurt.

According to a one-page statement, the police used their service weapons in the attack but were riding in personal vehicles rather than marked police vehicles.

“They were dressed in civilian clothing. But when they appeared before an investigator of the Public Ministry, they wore uniforms and came in their assigned patrol vehicles, attempting to hide their own vehicles and falsely cover up the circumstances of the attack,” the statement said.

The ambush was yet another example of how difficult it’s been for U.S. authorities to rely on Mexican law enforcement for assistance in combating drug-trafficking gangs in Mexico. The 35,000-member Federal Police force has received millions of dollars in U.S. assistance, and it’s considered a crucial tool in fighting organized crime. But the brazen ambush suggested that Mexican gangs had infiltrated the force.

In addition to the 14 police officers, prosecutors said they were likely to charge a civilian Federal Police employee – who rushed to the scene with an assault weapon after the attack – with illegal possession of a military weapon, the statement said. Another six officers were charged with either lying about what they knew or allowing those accused of carrying out the ambush to flee the scene, it said.

The embassy vehicle was traveling along a rutted two-lane road near the village of Huitzilac in Morelos state, about 50 miles south of Mexico City, when the ambush occurred. The Americans – U.S officials have never responded to questions about whether they worked for the CIA – were bound for a Mexican naval base tucked in hills where counter-drug training often takes place.

Common criminals and gangsters are active in the area. Days before the attack, kidnappers snatched a midlevel employee of the National Institute of Anthropology and History in what police described as an “express kidnapping” to extort money from worried relatives.

Lawyers for the accused officers have said the police were pursuing kidnappers and that they thought the embassy vehicle might have been carrying a kidnap victim.

Upon facing gunfire, the embassy SUV swung around and raced back to a federal highway that connects Mexico City with Cuernavaca, a colonial resort city that’s a weekend getaway for well-off Mexicans.

According to witnesses and news reports, other vehicles carrying plainclothes police joined in pursuit of the SUV, which bore clearly visible diplomatic license plates, firing at it until it halted on the highway in front of arriving law enforcement units that had been summoned to the rescue.

Mexican and U.S. officials have drawn a veil around the investigation into the attack, refusing to discuss it publicly or privately. A unit of FBI agents flew from Washington to help Mexican prosecutors mount a criminal case.