Mexican officials ruled out engine failure in the helicopter crash that killed the government's No. 2 official, saying Sunday that all evidence in the investigation so far points to an accident.
Civil aviation director Gilberto Lopez Meyer said at a news conference that a study of radar images led investigators to conclude that up to the last seconds of the helicopter's flight, its path did not change and conditions were normal.
Lopez said there were no signs the pilot lost control of the helicopter before it smashed into a mountainside south of the capital Friday morning.
Officials have blamed sudden foggy conditions, which they speculate forced the pilot to seek an alternate low route through the Ajusco mountain range.
Sixteen aviation experts are investigating the crash that killed Interior Minister Francisco Blake Mora and seven others, Transportation Secretary Dionisio Perez Jacome said at the news conference.
Three of them belong to the U.S. National Transportation Safety Board and two come from the U.S. Federal Aviation Administration. The agents arrived Saturday at the request of Mexico's government.
President Felipe Calderon appointed Mexico's transportation secretary to carry out a thorough investigation into the causes of the helicopter crash.
Mexico's Transportation and Communications Department will remain the lead investigative agency.
Federal prosecutors said they questioned a man Sunday about why he used Twitter to send a message before the helicopter crash warning Mexican officials who were flying to be cautious.
The Attorney General's Office said Mareo Flores, 26, was let go after questioning because prosecutors did not find any connection between his tweet and the interior secretary's death.
Flores had tweeted after the crash that his warning was just a coincidence. He said he was referring to the death of a former interior secretary, Juan Camilo Mourino, who died in a plane crash three years ago.
His warning had said: "I hadn't gone out so early since Mourino's small plane fell, be cautious flying officials."
Flores' brief detention sparked a number of comments on Twitter, most expressing surprise that his tweet was taken so seriously.