Story highlights Sen. Chuck Grassley said Monday that President Donald fired FBI Director James Comey on the advice of his deputy Attorney General.

Trump admitted last week that he would have fired Comey regardless of the recommendation.

(CNN) Republican Sen. Chuck Grassley said Monday that President Donald fired FBI Director James Comey on the advice of his deputy Attorney General, even though Trump admitted last week that he would have fired Comey regardless of the recommendation.

In initially explaining Trump's decision to fire Comey, Vice President Mike Pence and Deputy White House spokeswoman Sarah Huckabee Sanders both cited a memo from deputy Attorney General Rod Rosenstein that criticized Comey's handling of the investigation into Hillary Clinton's email server. Trump quickly contradicted that explanation himself in an interview with NBC's Lester Holt, saying, "Regardless of the recommendation I was going to fire Comey."

However, in an interview on Monday with Iowa local radio station KVFD 1400AM, Grassley, the chair of Senate judiciary committee, cited the Rosenstein memo as Trump's "main reason" for firing Comey.

"The President made his decision from reasons that are very special to him," Grassley to Iowa local radio station KVFD 1400am on Monday. "Taking advices (sic) as he did from the deputy Attorney General Rosenstein that Comey should not have acted both as a prosecutor and an investigator. In other words, he should be investigating the Justice Department, under then-(Attorney General) Lynch should have made the decision on prosecuting. He seemed to take responsibility for both, which I think is main reason the President made his decision."

Grassley said he had his own problems with Comey and said the FBI lacks transparency with respect to requests he has made.