"I'm very disgusted," Derek Maltz, who oversaw the Drug Enforcement Administration's investigation of Viktor Bout, told ABC News after Bout was traded for Brittney Griner. "It's really upsetting to me."
On Thursday, the WNBA star was swapped for Bout -- a Russian convicted arms dealer who spend 15 years in U.S. prison -- in an international prisoner exchange. Griner was serving a nine-year sentence in a Russian prison for possession of vaping cartridges containing hashish oil, which is illegal in Russia, before the exchange.
Maltz, in 2008, was the special agent in charge of the DEA's special operations division which took down Bout in a sting operation in Thailand.
"DEA was asked to help take this guy down because he was such a national security threat," Maltz said. "We at the DEA were just trying to step up to the plate and do the right thing for national security."
In November 2007, Bout agreed to sell DEA informants posing as FARC rebels in Colombia millions of dollars in weapons, including: 800 surface-to air-missiles; 30,000 AK-47s; 10 million rounds of ammunition; 5 tons of C4 plastic explosives; and ultra light airplanes outfitted with grenade launchers to attack U.S. helicopters in Columbia, according to Maltz.
"Viktor Bout was ready to sell a weapons arsenal that would be the envy of any small country," Maltz said.
Maltz said he has no issue with bringing home Americans and called this "a great day for Brittney Griner and for America" but he said the exchange for Bout would make things less safe for Americans traveling internationally.
"To make that exchange, all Americans are at greater risk with international travel," Maltz said, fearing it would promote taking American citizens captive.