Two flight recorders from a plane crash that killed Mexico's No. 2 government official were sent to the U.S. for examination, officials said Thursday, amid widespread speculation — but no evidence — that drug cartels were to blame.

Both "black boxes" were found where the Learjet 45 slammed into rush-hour traffic in a posh Mexico City neighborhood, Transportation Secretary Luis Tellez said at a news conference. Five people on the ground and nine people on the plane were killed in Tuesday's crash, including Interior Secretary Juan Camilo Mourino.

Officials say they have few clues why the plane suddenly dropped from the evening sky.

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But they have been unusually open in publicizing details of the investigation, trying to discourage conspiracy theories that thrive in a country on edge from relentless news of drug-related shootings, kidnappings and beheadings. The violence has surged during a two-year-old army and police offensive to wrest control from drug cartels.

The 37-year-old Mourino, one of President Felipe Calderon's closest confidants, was Mexico's equivalent of vice president and domestic security chief. Also on the plane was former anti-drug prosecutor Jose Luis Santiago Vasconcelos, who had been the target of at least one assassination attempt.

"Nobody is more interested than me in the truth emerging and the cause of this incident being cleared up," Calderon said at a memorial ceremony for the dead.

Tellez said experts would need at least a week to analyze the plane's voice and data recorders for clues to what went wrong.

The crash occurred in clear weather, and in their last recorded radio conversation, the plane's flight crew calmly discussed radio frequencies and speed with controllers. The tape went silent just as radar lost the plane's altitude reading.

"Everything was normal on the flight, and a few seconds before the accident, something happened that significantly altered" the situation, said Gilberto Lopez, a pilot overseeing the probe. "At this moment, all the possibilities are potentially important."

He said experts are following the normal lines of investigation for any crash, including possible human error, mechanical failures, maintenance problems or turbulence caused by other aircraft.

Experts from the U.S. National Transportation Safety Board, the U.S. Federal Aviation Administration and Britain's Civil Aviation Authority are in Mexico helping with the investigation.

In an editorial Thursday, El Universal newspaper urged people to wait for results of the investigation before jumping to conclusions. But it also noted that Mexico's "history is filled with assassinations that have never been cleared up or whose resolution does not deserve the trust of public opinion."