Argentina police had seen Leaitua meet with the drug associates in late August 2011.
"There's no doubt that in the Crown submission that the accused was an active player."
Mr Snelgar said Leaitua "aided and assisted" the importation, so he could be guilty of importing cocaine as a party.
Defence lawyer Chris Wilkinson-Smith suggested Ms Vega, who was younger than Leaitua despite being his mother-in-law, was acting alone, saying she voluntarily swallowed the cocaine.
Leaitua, his partner and their two children were simply travelling back to New Zealand to live. They were from Colombia, but had to go to Argentina for appropriate entry documents, Mr Wilkinson-Smith said.
He said they were then stuck there for two months because a volcanic eruption scuppered their initial flight plans.
He said the jury would have to consider if Leaitua and his family knew of Ms Vega's offending.
The Crown is expected to call 29 witnesses, including Argentinian police officers, in a trial scheduled to last three weeks.