MEXICO CITY (AP) — The turbulent wake of a large passenger plane likely caused the fatal crash of a government jet carrying Mexico’s second most powerful official, the transportation secretary said Friday.

A preliminary investigation found the jet’s pilots didn’t immediately follow instructions to slow down and appeared to be nearly one nautical mile too close behind a Boeing 767-300 on the same flight path to Mexico City’s international airport, Luis Tellez announced at a news conference.

Tellez said the planes were 4.15 nautical miles apart, and that international standards recommend at least 5 nautical miles to avoid dangerous wake turbulence — unstable air that can make it very difficult to control a plane, especially when slowing down for a landing.

A black box recording revealed the pilots lost control seconds before the jet smashed into rush-hour traffic on Nov. 4, narrowly avoiding tall office buildings in a posh Mexico City business district. The investigation found no sign of foul play, and the flight was normal until only seconds before it dropped out of the sky at a 42 degree angle.

A video camera on a nearby building caught the plane’s horrifying plunge, officials said.

Tellez also said there were indications the pilots may have lacked training — that they seemed unfamiliar with the controls of the Learjet 45.

Interior Secretary Juan Camilo Mourino and eight others were killed. The crash also set fire to cars and killed five people on the ground.

The Mexican government said from the start that it appeared to be an accident, but it has held a very public investigation, carefully showing why it has ruled out sabotage. Many Mexicans distrust their government, and rumors are widespread that the jet was targeted by powerful and increasingly violent drug cartels.

Mourino was the equivalent of Mexico’s vice president and one of the closest confidants of President Felipe Calderon. Also killed was former anti-drug prosecutor Jose Luis Santiago Vasconcelos, who had been the target of at least one previous assassination plot.

Officials called in foreign investigators including U.S. National Transportation and Safety Board experts, who last week ruled out a bomb, saying no trace of explosives were found at the scene.

The crash occurred in clear weather, and in their last recorded radio conversation with the control tower, the plane’s flight crew calmly discussed their radio frequencies and speed just before dropping off the radar.