Hennepin County Attorney Mike Freeman on Monday called for Sen. Amy Klobuchar to request a federal investigation into a years-old murder case that dogged her in the final days of her presidential bid, pushing back on her request for him to seek an outside review.

The move comes days after Klobuchar urged Freeman, her successor, to call for an independent review of the case against Myon Burrell, who was convicted in the 2002 killing of 11-year-old Tyesha Edwards. Klobuchar did not specify what agency she thought should look into the matter.

Burrell was convicted under Klobuchar’s tenure as Hennepin County attorney and again under Freeman’s tenure after he was granted a new trial.

Freeman noted in a letter to Klobuchar on Monday that only the U.S. Justice Department would have the resources to independently review a case that includes 30,000 pages of documents plus videotaped evidence. Freeman also stressed that his office began its own review about seven months ago and would cooperate with any new federal probe. But he put the onus on Klobuchar to call for an outside review.

A spokesman for Klobuchar’s office said they are reviewing the letter and had no further immediate comment.

Burrell’s case became an issue for Klobuchar’s presidential campaign in February when an Associated Press investigation raised questions about apparent failings in the police work. An AP story also quoted a man who said he, not Burrell, fired the shot that killed Tyesha, a Minneapolis girl who was struck while doing homework at the dining room table. The shot was meant to scare a rival and instead penetrated a nearby home and struck Tyesha, an innocent bystander.

The latest exchange suggests a growing disagreement between Freeman and Klobuchar in the controversial conviction of Burrell, who is serving a life sentence in the murder. Burrell, now 33, was 16 when he was first convicted in Tyesha’s killing, and continues to maintain his innocence. A group of Twin Cities civil rights activists had pressed Klobuchar to abandon her White House bid until the case was resolved, forcing the cancellation of one of her last campaign events.

Freeman has defended Klobuchar’s handling of the case, urging people not to turn the matter into a “political football.” He also implored critics to direct their questions to his office.

In the letter, which he did not release publicly, Freeman also cited a district court order and Minnesota Supreme Court opinions that detail the evidence and testimony in the two trials in which Burrell was found guilty. “Those filings provide a full picture of why he was found guilty and why, ultimately, his conviction was upheld,” his office said in a statement.

At the same time, Freeman has resisted Klobuchar’s suggestion in her letter last week that he pursue an independent investigation by an agency outside his office. Klobuchar’s request earned praise from activist Nekima Levy Armstrong, who was among the protesters at a March 1 rally for Klobuchar in St. Louis Park. Klobuchar, trailing in the race for the Democratic presidential nomination, ended her campaign the next day.