A former federal prosecutor explained why some Trump associates -- including the president’s eldest son -- should be especially worried about special counsel Robert Mueller.

Daniel Goldman, the former Assistant US Attorney for the southern district of New York, told MSNBC’s “Morning Joe” earlier this week that Mueller may not even need to follow up on written answers submitted this week by President Donald Trump as part of the Russia probe.

“They don't need his answers,” Goldman said Wednesday. “So if he doesn't want to answer the questions and defend himself on an obstruction justice case, then he doesn't have to.”

MSNBC contributor Natasha Bertrand pointed out that Mueller hadn’t even questioned Roger Stone, a longtime Trump associate with links to Wikileaks and its founder, and Goldman said both men should be particularly worried.

“We now think Julian Assange, there's an indictment somewhere sealed against him,” Goldman said. “His lawyers on television saying no one has talked to us, Roger Stone, no one has talked to Roger Stone.”

He explained why that silence should concern Stone and Assange -- and Donald Trump Jr., who also has not been contacted by the special prosecutor.

“Anyone who is the subject of an investigation should worry if prosecutors don't want to talk to them, because that means that they are circling around you,” Goldman said. “That's pretty well accepted.”