Harare - A member of parliament in Zimbabwe says he wants parliament to summon former president Robert Mugabe to explain where $15 billion worth of diamond revenue went to during his rule, according to a report.Temba Mliswa, a former ruling party MP turned independent, chairs a parliamentary committee on mines that has been probing diamond mining in Zimbabwe’s once-booming eastern Chiadzwa diamond fields.Grace links?Two years ago Mugabe told state TV that the country had earned less than $2 billion from its diamonds - but an estimated $15 billion worth had been mined. The former president’s wife Grace was at one time rumoured to be linked to one of the main diamond firms operating in Chiadzwa, though the association was never proven.Mliswa also said Mugabe would be grilled on why his government chose to evict firms from the diamond fields to make way for a state-run diamond firm in February 2016.'Investors were putting in the money'"If we have to bring the former president before us, he will come so that he tells us where he got the 15 billion-dollar figure, why the government took over diamond mines yet investors were putting money,” Mliswa was quoted as saying by online news site, New Zimbabwe. "We never saw that money in the fiscus," the MP added.Mugabe was persuaded to step down after the military put him under house arrest in November 2017. There’s no guarantee he would agree to appear before the committee.KEEP UPDATED on the latest news from around the continent by subscribing to our FREE newsletter, Hello Africa.FOLLOW News24 Africa on Twitter and Facebook.