The American pilots of an executive jet could be charged with manslaughter if they are considered responsible for a high-altitude crash with a Boeing-737-800 that killed 155 people, federal police said Wednesday.

Police earlier seized the passports of pilots Joseph Lepore and Jan Paladino to prevent them from leaving the country.

Lepore and were piloting the Brazilian-made Legacy 600 when it struck a Boeing 737-800 over Mato Grosso state in the Amazon rain forest. The Boeing crashed, killing all 155 aboard. The Legacy landed safely at an air force base.

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"We have received an order from the Federal Prosecutor's Office in Mato Grosso to begin investigating the possible commission of a crime inside the aircraft. The investigation begins today," said Geraldo Pereira, acting director of the Federal Police in Mato Grosso, speaking by phone.

"We will start investigating if the two pilots caused the accident and if they are proven guilty they could be charged with involuntary manslaughter," Pereira said.

Investigators are puzzled why the pilots weren't alerted by equipment designed to avoid collisions. The air force said both jets were equipped with a Traffic Collision Avoidance System, or TCAS, which monitors other planes and sets off an alarm if they get too close.

"Preliminary investigations indicate that the pilots may have turned off the transponder" that communicates the plane's location, he said. "They knew the risks they were running and nevertheless they took certain attitudes that endangered the lives of people."