Former British spy Christopher Steele, the author of the now-infamous anti-Trump dossier, must be asked several key questions by American investigators, Alan Dershowitz told Fox News Wednesday.

Dershowitz told "Hannity" that he is pleased the former MI6 agent agreed to be questioned by U.S. investigators, who Dershowitz said must ask Steele when or whether he began to doubt the veracity of his information.

"I'm glad that he is testifying or at least appearing in front of the Justice Department," the Harvard Law professor emeritus said. "I think the questions that they will put to him in order to try to protect the investigation will be based on chronology - When did you realize that the report wasn't as valid and solid as you originally thought it was? When did you learn that it was paid for by Democrats?"

DOSSIER AUTHOR CHRISTOPHER STEELE WILL BE QUESTIONED BY US INVESTIGATORS: REPORT

Steele compiled the Trump dossier for opposition research firm Fusion GPS, which was a client of Hillary Clinton's presidential campaign in 2016.

"What [Steele] said up until now is 'the report itself is not valid'," Dershowitz claimed. "But what we need to know is, 'when they knew it' and 'what they did about it'."

"And, did anybody misrepresent what they knew at any particular time to the FISA [Foreign Intelligence Surveillance] court?" he continued.

The Times of London cited sources close to Steele in reporting he will be interviewed by American investigators in London within weeks.

The development comes as attention has returned to the dossier authored by Steele -- especially since its more sensational claims were not substantiated by Special Counsel Robert Mueller, whose report found no evidence of collusion between the Trump campaign and Russia during the 2016 election.

The paper did not specifically say who would interview Steele.

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But there are several ongoing investigations in the U.S. related to the origins of the Russia probe, and federal investigators are probing how the Democrat-funded anti-Trump dossier written by Steele was used to secure surveillance warrants for former Trump campaign adviser Carter Page in 2016.

Fox News' Alex Pappas contributed to this report.