Mr. Smith died at age 81 on May 14, which was about 10 days after the Journal interviewed him. His account of the email search is believed to be his only public comment on it.
The operation Mr. Smith described is consistent with information that has been examined by U.S. investigators probing Russian interference in the elections.
Those investigators have examined reports from intelligence agencies that describe Russian hackers discussing how to obtain emails from Mrs. Clinton’s server and then transmit them to Mr. Flynn via an intermediary, according to U.S. officials with knowledge of the intelligence.
In the interview with the Journal, Mr. Smith said he and his colleagues found five groups of hackers who claimed to possess Mrs. Clinton’s deleted emails, including two groups he determined were Russians.
“We knew the people who had these were probably around the Russian government,” Mr. Smith said.
In phone conversations, Mr. Smith told a computer expert he was in direct contact with Mr. Flynn and his son, according to this expert. The person said an anti-Clinton research document prepared by Mr. Smith’s group identified the younger Mr. Flynn as someone associated with the effort. The expert said that based on his conversations with Mr. Smith, he understood the elder Mr. Flynn to be coordinating with Mr. Smith’s group in his capacity as a Trump campaign adviser.