Heather Bennett told CNN members of Mugabe's Zanu-PF party offered to release imprisoned opposition leaders in exchange for a promise of amnesty for any crimes between Zimbabwe's independence in 1980 and 2009.
Her husband, Roy Bennett, was arrested on terrorism-related charges shortly before he was to be sworn in as deputy agriculture minister. He said he rejected taking part in such a deal.
There has been no official word on the alleged offer.
Bennett, a long-time Mugabe foe, has been charged with illegally possessing firearms for the purposes of trying to commit acts of insurgency, banditry and terrorism and to illegally leave the country, his lawyer said.
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