The Wanganui man gave officials permission for his bag to be opened.
"We only found one black jacket and then the bag was already empty," Mr Leonard is reported as saying.
"But when we had it X-rayed again, there was still this suspicious appearance, like a lump, while it was supposed to be empty because the jacket had been taken out."
The bag was taken to a 'checking room', where all the contents were taken out of pockets and compartments, the official said, with de Malmanche present.
It was then that officers found a plastic bag wrapped with tape containing crystals which tested positive for methamphetamine, the AAP reported.
De Malmanche claimed he did not know what the package was, Mr Leonard told the court.
"We can say that he was suspicious because the defendant's jacket was soaked wet because of sweat," Mr Leonard said.
"During the X-ray checking, the defendant put his jacket into his bag. In that cold airport, the defendant shouldn't have been sweating like that."
The trial continues next Thursday.
The New Zealander is in Kerokoban Prison, and faces the death penalty if found guilty.
The defence - including New Zealand lawyer Craig Tuck - tried unsuccessfully to have the trial aborted, questioning a "raft of issues" with the indictment, but judges have ruled the trial should proceed.
It is expected the prosecution will take four to five weeks to present its case, after which the defence will present its version of events, which Mr Tuck has previously said could take eight weeks.
The defence has said de Malmanche was a "trafficked person not a trafficker". It's a defence Mr Tuck has said could be groundbreaking.
A defence team of about 10, including a British QC, Indonesian lawyers and human rights experts, are working on the case.
