Mexico City ? U.S. aviation officials joined their Mexican counterparts Wednesday in trying to determine what caused the crash of a government jet that killed two of the nation’s top anti-drug officials and touched off speculation of a possible criminal role.

With unprecedented swiftness, Mexican authorities publicly played the conversations among the Learjet pilots and the control tower – those recorded in the “black box” – less than 24 hours after the Tuesday crash.

The conversations and radar tapes from the control tower showed the craft suddenly falling off the screen with no calls of alarm after what appeared to be a normal descent toward the capital’s airport seven miles away, officials said.

Instead, the craft went into free-fall, slamming into parked cars just a block from rush-hour traffic along a major thoroughfare. All nine plane occupants and six people on the ground died.