AUGUSTA – When authorities found 146 marijuana plants growing inside the secure, fenced-in area at the Augusta State Airport last summer, they set up a camera to find the illegal gardeners.

Marlon Cloutier, 47, of Augusta and an unidentified man were seen tending to the plants.

When Cloutier was interviewed by Maine Drug Enforcement Agency officers on Aug. 16, he confessed almost immediately, according to documents unsealed recently in U.S. District Court in Portland.

Cloutier, convicted on six arson charges two decades ago and ordered to repay more than $126,000 in restitution, told officers he and the other man planned to sell the marijuana because they needed money.

“They had previously grown marijuana near the airport but had it stolen, and he thought discovery of the marijuana plants would be less likely if the plants were inside the airport fence,” Assistant U.S. Attorney David Joyce wrote in the prosecution’s version of events.

John Guimond, the airport manager, said Wednesday it came as a surprise to him when he was told about the operation several months later.

“It’s in an area that you couldn’t see from up above, in a thick pine grove area, not up on the plateau where the airport is,” Guimond said of the place where the marijuana patch was found, on the northeast side of the airport.

Guimond said he was told police were called after someone along the Nordic trails of the Bond Brook Recreation Area saw a man go into the woods and became suspicious when he did not re-emerge for some time.

Augusta police officers conduct sporadic patrols of the airport perimeter, Guimond said.

Cloutier signed a document in October pleading guilty to the marijuana charge from August and to possessing 21/2 ounces of cocaine in South Portland on May 5, 2011. He faces a minimum five-year prison term in connection with the federal offense of conspiracy to manufacture 100 or more marijuana plants.