Republican Senator Tom Cotton questioned Democratic presidential nominee Hillary Clinton's qualifications to hold the United States' top office, saying Sunday that emails on her private server about an Iranian nuclear scientist who was executed for spying for the US show she's "reckless."A spokesman for Iran's judiciary said on Sunday that the country had executed Shahram Amiri, who was detained in 2010 when he returned home from the United States, after a court convicted him of spying for Washington.Speaking in an interview with CBS's Face the Nation, the Arkansas Senator said, "I'm not going to comment on what he may or may not have done for the United States government, but in the emails that were on Hillary Clinton's private server, there were conversations among her senior advisers about this gentleman," Cotton said on CBS's "Face The Nation." "That goes to show just how reckless and careless her decision was to put that kind of highly classified information on a private server and I think her judgment is not suited to keep this country safe," he added.Amiri, a university researcher working for Iran's Atomic Energy Organization, disappeared during a pilgrimage to Saudi Arabia in 2009, and later surfaced in the United States. He returned to Iran in 2010 and received a hero's welcome before being arrested.A US official said in 2010 that Washington had received "useful information" from Amiri.Iran had accused the CIA of kidnapping Amiri. US officials said Amiri had been free to come and go as he pleased, and that he may have returned because of pressures on his family in Iran. Amiri had denied this, saying "my family had no problems". In a video aired by Iranian state TV in 2010, Amiri said he had fled from US agents.Cotton spoke in reference to two emails about Amiri that were sent to Clinton's private server during her tenure as Secretary of State. Politico quoted Clinton aide Jake Sullivan as writing in a 2010 email: “The gentleman you have talked to [top State Department official] Bill Burns about has apparently gone to his country's interests section because he is unhappy with how much time it has taken to facilitate his departure...This could lead to problematic news stories in the next 24 hours. Will keep you posted."Politico quoted energy envoy Richard Morningstar as writing in another email: "Per the subject we discussed, we have a diplomatic, 'psychological' issue, not a legal issue...Our friend has to be given a way out. We should recognize his concerns and frame it in terms of a misunderstanding with no malevolent intent and that we will make sure there is no recurrence. Our person won't be able to do anything anyway. If he has to leave, so be it."Clinton has come under fire for using a private email server during her tenure as secretary of state in US President Barack Obama's first term.FBI Director James Comey said last month that the FBI had found evidence that "the security culture of the State Department in general, and with respect to use of unclassified systems in particular, was generally lacking in the kind of care for classified information that's found elsewhere in the US government."However, he recommended against prosecuting Clinton or her aides for their "extremely careless" handling of classified information on the private email server that she used as secretary of state.