The little-known, yet wide-reaching super PAC that spent millions of dollars promoting Democrat Doug Jones in Alabama’s Senate race has been found to be funded heavily by the Democratic Senate Majority PAC.

Highway 31, a group responsible for widespread campaign mailers, phone calls and advertisements for Jones, didn’t have to disclose donors during the campaign despite spending more than $4 million because of how the election’s reporting and payment schedules were structured.

Chris Hayden, spokesman for the Senate Majority PAC, said Tuesday that the group “predominantly funded” the PAC called Highway 31, which sent out advertising and mailings to help defeat Republican Roy Moore and spent about $6 million in Alabama.