WASHINGTON (Reuters) - Former FBI Director James Comey offered some advice on Monday for Special Counsel Robert Mueller: Press President Donald Trump to sit down for a completely “open-ended” interview in the probe of alleged Russian meddling in the 2016 election.

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“In any interview with a subject, I would want to make sure I had unlimited time,” Comey said, when asked his opinion during a packed event at George Washington University sponsored by a local bookstore.

Comey said the ideal parameters would include an interview that is “open-ended as to time, open-ended as to subject” and ensure the person had a “clear understanding that you are obligated to tell the truth and failure to do so would be at your peril.”

Comey’s firing by Trump last May paved the way for Deputy Attorney General Rod Rosenstein to hire Mueller to investigate the meddling allegations and possible collusion between Trump’s campaign and Russia. Mueller is also probing whether Trump obstructed the investigation.

Comey, who took detailed notes of his interactions with Trump, said later he believed Trump fired him to undermine the FBI’s Russia probe.

Russia has denied interfering in the election. Trump has denied any collusion or improper activity and called the Mueller investigation a witch hunt.

Previously, Trump said he would be willing to sit down for an interview under oath with Mueller.

But a recent FBI raid on the offices and home of his personal lawyer Michael Cohen could make that less likely.

Trump has since added former New York Mayor Rudy Giuliani to his legal team to help deal with Mueller’s investigation.

Speaking before a friendly audience, which often broke into applause, Comey spoke about his observations of Trump, Mueller’s investigation and the impact Trump’s presidency is having on the American political landscape.

He said that in a normal environment, a sitting president would not be able to avoid an interview about his conduct.

“As an American citizen, I would expect my president to respect the rule of law ... and to cooperate with a lawful, appropriate investigation,” he said.

Monday’s event was the latest in a series of media interviews that Comey has given in connection with his bestselling book, “A Higher Loyalty: Truth, Lies, and Leadership.”

Trump and other Republicans have blasted Comey and challenged assertions he made in the book.