ABC News' Michael Falcone reports:

Although the origins of the leaked video of Mitt Romney's May fundraiser remain shrouded in mystery, one of the intermediaries involved in negotiating the tape's release acknowledged on Tuesday it was not one of Romney's donors who shot it.

James Carter IV, an Atlanta-based Democratic opposition researcher and the grandson of former President Jimmy Carter said it would be "fair to assume that" the person who filmed Romney was not one of the paying guests at the candidate's $50,000-a-plate fundraiser in Boca Raton on May 17.

"I found a piece of the longer video during a routine search on YouTube that I do, and tracked it down to its source and talked them into giving it up," Carter said in an interview with MSNBC's Chris Matthews.

Carter worked with Mother Jones Washington editor David Corn to obtain a complete copy of the hidden-camera video that captured Romney's candid comments at the high-dollar event hosted by businessman Mark Leder. Mother Jones posted the videos in two installments on Monday and Tuesday, including the full tape this afternoon.

The angle of the hidden camera shows Romney from his left side and the recording device appears to be place somewhere on a table that wait staff are seen using to deposit napkins and decanters of red wine. In the foreground, several donors sit at a table listening to Romney speak at the front of the room.

When asked about the leaker's motivations in taping Romney, Carter said: "They thought that some of the things that Romney was saying in the video needed to be heard by a wider audience."

According to reports, Carter said he had been in delicate negotiations with the Twitter user "Anne Onymous" ( @AnneOnymous670) who had been tweeting out the videos since late August. He eventually reached an agreement with the leaker.

Carter also acknowledged that Romney's disparaging comments about his own grandfather did not go unnoticed during his pursuit of the footage that has rocked the political world for the last 48 hours.

"That is not something that I think favorably about him for," he told Matthews.