Special counsel Robert Mueller on Friday filed his response to former national security adviser and cooperating witness Michael Flynn’s sentencing memo. Flynn pleaded guilty to lying to the FBI last year about his contacts with Russian officials and is set to be sentenced on Dec. 18.

In their own memo filed Tuesday, Flynn’s defense attorneys asked he be spared prison time for his “uncharacteristic error in judgment.” They suggested that federal agents may have lured him into a false sense of security before he agreed to the Jan. 24, 2017 interview about his communications with Russians, failing to notify the retired general that it is a crime to lie to the FBI.

Mueller came out swinging against that argument in his response, saying “nothing about the way the interview was arranged or conducted caused the defendant to make false statements to the FBI.”

“A sitting National Security Advisor, former head of an intelligence agency, retired Lieutenant General, and 33-year veteran of the armed forces knows he should not lie to federal Agents,” Mueller said. “He does not need to be warned it is a crime to lie to federal agents to know the importance of telling them the truth.”

Mueller rejected Flynn’s argument that the circumstances of the interview should be a mitigating factor in determining his sentence, urging the court to “reject the defendant’s attempt to minimize the seriousness of those false statements.”

Mueller said in a filing earlier this month that Flynn offered “substantial” cooperation to his investigation over the past year, and recommended that he serve no time behind bars.

In the latest document, the special counsel takes a firm tone with Flynn for implying there was anything untoward about the FBI’s conduct towards him. Mueller notes that Flynn also falsely told the Washington Post, Vice President Mike Pence, then-Chief of Staff Reince Priebus and then-Press Secretary Sean Spicer that he did not discuss sanctions with the then-Russian Ambassador to the U.S. before President Trump took office.

“By the time of the FBI interview, the defendant was committed to his false story,” Mueller said.

Former FBI Deputy Director Andrew McCabe also notified Flynn about the topic of the interview—what McCabe called “his recent contacts with Russian representatives”—before Flynn sat down with agents, according to contemporaneous notes made by McCabe and submitted by Mueller to the court.

“The interview was voluntary, and lacked any indicia of coercion,” Mueller said.

The agents even tried to signal to Flynn that they were aware of the exact nature of his contacts, according to the document.

“When the defendant said he did not remember something they knew he said, they used the exact words the defendant had used in order to prompt a truthful response,” Mueller wrote.

In something of a warning shot, Mueller concluded the filing by said that Flynn’s cooperation and military service still merit a light sentence—“assuming the defendant continues to accept responsibility for his actions.”

Read the memo and two exhibits submitted by the special counsel below.