A senior U.S. official tells the Associated Press there is strong circumstantial evidence that Mexican federal police who fired on a U.S. Embassy vehicle five weeks ago, wounding two CIA officers, were working as assassins for organized crime.

A Mexican official well informed on the Aug. 24 ambush confirmed to the AP Tuesday that prosecutors are investigating whether the Beltran Leyva Cartel was behind the attack.

The Mexican said that is one among several tracks of investigation into the shooting up of an armored SUV that was clearly marked with diplomatic license plates on a rural road near Cuernavaca south of Mexico City. Federal police, often accused  of infiltration and corruption by drug cartels, have said the shooting was a case of mistaken identity as officers were looking into a kidnapping.

"That's not a `We're trying to shake down a couple people for a traffic violation sort of operation. That's a `We are specifically trying to kill the people in this vehicle'," a U.S. official familiar with the case told the AP. "This is not a `Whoops, we got the wrong people.' "

Asked if the Mexican police in the shooting were tied to organized crime, the U.S. official said, "The circumstantial evidence is pretty damn strong."

A federal police spokeman Tuesday maintained the position that their agents fired by mistake. The U.S. State Department would not comment.