LA PAZ, Bolivia (AP) — A Bolivian judge on Thursday ordered that the head of the ill-fated chartered airline whose plane crashed in the Andes last week be detained while authorities investigate him for possible charges of manslaughter and other crimes.

Gustavo Vargas, a retired air force general who is CEO of the LaMia airline, complained at the court hearing that he is being unfairly blamed for the November 28 crash near Medellin, Colombia.

Authorities have said it was a preventable tragedy that took the lives of all but six of the 77 people on board the LaMia plane, including members of a Brazilian soccer team heading to Colombia for the finals of a South American championship.

“The prosecutors are liars,” said a defiant Vargas, who denied any wrongdoing. “The prosecutors can’t blame me. They know there are two owners.”

The judge’s ruling to keep Vargas locked up came as a Bolivian aviation official who fled to Brazil after authorities began investigating why she signed off on the aircraft’s flawed flight plan accused her bosses of trying to stage a cover-up.

Until the crash, Celia Castedo was an unknown veteran employee at the regional office of the agency responsible for controlling Bolivia’s air traffic.

She was thrust into the spotlight of the five-nation crash investigation after a copy of the flight plan with her signature emerged showing the British-built short-range jetliner was allowed to depart Santa Cruz, Bolivia, with barely enough fuel to complete the more than four-hour flight to Medellin, a flagrant violation of international air norms.

In a letter to Bolivian media made public Thursday, Castedo said that far from authorising the flight, she tried to stop it. She claimed to have authored an internal report in which she recounted how she sternly asked the airline’s dispatcher on three occasions to fix the flight plan.

She said that the day after the crash, superiors who she did not identify “harassed and pressured” her to modify the report, which has been circulating for days in Bolivia media but whose authenticity has yet to be verified. She said her signature and stamp on the flight plan was a mere formality acknowledging receipt, saying another government office, Bolivia’s civil aviation agency, is exclusively responsible for authorising international chartered flights.

Castedo, who Bolivian officials have said was immediately suspended and put under investigation, said she sought asylum in Brazil because her rights to a fair defence couldn’t be guaranteed.

Authorities have cast doubt on Castedo’s version of events.

“There were no observations made to the flight plan,” Public Works Minister Milton Claros said, accusing Castedo of fabricating the document after the crash to cover up her own missteps and negligence.

Aviation experts have also criticised Castedo’s actions, saying she could have stopped the flight if she had wanted to.

“No pilot can impose their will,” said Jorge Valle, an aviation lawyer in Bolivia who until 2007 served as president of the agency where Castedo worked.

“It’s her word against that of a dead man,” Valle said, referring to the airline’s flight dispatcher, who was killed in the crash.