The list of analysts who made those claims includes this former NSA offical
Bill Binney. See excerpt below.
And I believe the team even went so far to state that the timings indicate only a physical connection to the server was used - ie not even a local network. The evidence they presented indicates no possibility of an outside hack.
Binney claims the U.S. intelligence community's assessment that Russia interfered in the 2016 presidential election is false, and that the DNC e-mails were leaked by an insider instead.[22][23][24] He has appeared on Fox News at least ten times between September 2016 and November 2017 to promote this fringe theory.[17][22][23] Binney said that the "intelligence community wasn’t being honest here".[22] He has also been frequently cited on Breitbart News.[17] In November 2017 it was reported that a month earlier, Binney had met with CIA Director Mike Pompeo at the behest of President Trump.[22]
Binney has said he voted for Trump in the 2016 presidential election, calling Hillary Clinton a "war monger".[17