GREENS senator Sarah Hanson-Young's claim that she was spied on by Wilson Security during a visit to Nauru has been backed by former detention centre guards.
One guard told the ABC's 7.30 program a comprehensive surveillance operation involved up to eight members of the Emergency Response Team over the Senator's three-day stay in December 2013.
That is at odds with evidence given to a parliamentary inquiry by Wilson executives who conceded the operation took place, but said it was confined to an unauthorised observation from the car park for 12 hours.
In June this year when the allegations came to light, Prime Minister Tony Abbott dismissed the spying claim.
Immigration Minister Peter Dutton ridiculed her, saying the allegations were unfounded and she got her "facts wrong most of the time".
"I think Senator Hanson-Young conducts herself in a way which is frankly an embarrassment to our country," Mr Dutton said.
The whistleblower accused Wilson of repeatedly misleading the Senate inquiry, including that alcohol testing of staff was conducted daily.
He said he had not witnessed alcohol testing during his time working on Nauru.
He said the individuals and supervisor involved were called into the Wilson office and "told to shred pages from their notebooks and any reports they had written up".
Several former guards told the ABC of a culture of shredding reports.
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