Former Gov. Bill Richardson said Sunday he is “cautiously optimistic” that Americans Brittney Griner and Paul Whelan will be released and gave the timeline as ‘end of the year.’ The unofficial diplomat says he met with senior Kremlin officials and they seemed willing to talk.

Bill Richardson.

You might remember his name from his success in securing the release of American prisoners from countries such as Iran, North Korea and Sudan, though he has done it as a private citizen behind the scenes.

While Richardson also said that he’s working with the families of both Americans and coordinating with the White House for their release, the White House has not acknowledged his efforts. In fact, just last month, John Kirby, the former Pentagon press secretary, urged Richardson and other private citizens not to negotiate on behalf of the U.S. government.

“I respect that. I think any decision, for instance, release of prisoner exchange, has to be made by the president,” Mr. Richardson said.

But he insisted that there was still value for him and other like-minded individuals to continue pushing for Ms. Griner’s release in private channels.

“There are a lot of nervous Nellies in the government that think they can know it all, and that’s not the case,” he said. “Look at my track record over 30 years — I’m going to continue these efforts.”