"Are you sure this is a bad guy?" an American said at another point, with the American pilot telling his co-pilot "I think we're making a mistake."
Veronica Bowers, a Michigan missionary, and her 7-month-old daughter, Charity, were killed in the 20 April incident that has led to the suspension of a highly lauded US-Peruvian programme to force down suspected drug-smuggling flights.
Controversy still surrounds the incident with US officials claiming that the American crew had tried to stop Peruvian authorities from shooting at it.
Concern expressed
Officials who have seen a transcript of audio tapes of what happened in the minutes before the incident say the Americans repeatedly expressed concerns that the plane did not appear to be involved in drug trafficking.
Unlike most drugs flights it was flying straight, level and well inside Peruvian territory, not low, evasive and hugging the border for a quick getaway.
"Are you sure this is a bad guy?" an American said at another point, with the American pilot telling his co-pilot "I
think we're making a mistake."
Despite their reservations the crew did pass on the location of the plane to the Peruvian authorities.
Peruvian officers contacted on the ground about the Cessna said they were unable to locate a flight plan for the plane, so they sent up an A-37 jet that flew near the Cessna and visually noted its tail number, OB1408.
The Americans recommended that the Peruvians try to contact the Cessna by radio, and urged that no hostile action be taken unless the Cessna tried to take evasive manoeuvres.
Opened fire
The Peruvian officer on board, meanwhile, urged the fighter to fire warning shots if the aircraft ignored instructions to land.
After the jet opened fire, the pilot of the missionary plane, Kevin Donaldson, could be heard shouting, "They are killing us!" as he spoke with the air control tower in the city of Iquitos.
Mr Donaldson managed to land the plane, which is fitted with pontoons to land on water, on the Amazon River, and survived, along with Veronica Bowers' husband, Jim, and their 6-year-old son, Cory.
The tape did not make it clear whether warning shots were fired.
Peruvian air force officials have asserted that the pilot followed proper procedures, only shooting after the missionary aircraft failed to identify itself.
'No warning given'
But the missionary group that the Bowers worked for says the air force jet opened fire without warning or making contact with the Cessna, and asserts that the missionaries did file a flight plan, posting what they said was a copy of it on their website.
"When they attacked Kevin's plane, it was not an hour when the drug planes would be flying, especially the route he was in, a well known route not on the border," said Fred Mortimer, an Evangelical missionary from Wisconsin who has been in Peru's jungle since 1987.
"The plane was marked clearly. So many things just don't make sense."
The CIA has now debriefed the American crewmen and concluded they handled their role properly.
Suggestions that the American crew's lack of proficiency in Spanish could have created a communication problem have been dismissed by a US intelligence official, who said that that the Peruvian on board is bilingual and had passed a language test just days before the incident.