Baltimore's police commissioner asked the FBI on Friday to take over an investigation into the fatal shooting of a city homicide detective on the eve of his scheduled testimony to a federal grand jury looking into alleged police corruption.

Commissioner Kevin Davis made the request a day after a U.S. District Court grand jury in Baltimore indicted former Sgt. Wayne Jenkins on charges of duping colleague Sean Suiter in 2010 into "discovering" drug evidence Jenkins had planted in a car.

Davis said police, the FBI and federal prosecutors don't believe there's a connection between Suiter's planned testimony and his death Nov. 15.

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The FBI says it is aware of the request but is not commenting further, CBS Baltimore reports.

Davis suggested at a news conference, however, that the FBI and U.S. attorney's office haven't been forthcoming with information that could help his investigators in probing Suiter's shooting.

Baltimore authorities have said Suiter, 43, was fatally shot with his own gun after approaching a suspicious man in a vacant lot.

"Right now, there is no DNA evidence or other forensic evidence — blood, etc. — that identifies the perpetrator," Davis said.

"The circumstances surrounding Detective Suiter's killing are significantly complicated by the fact that he was to appear before a federal grand jury the following day," Davis wrote in a letter Friday to FBI Director Christopher Wray. "I am growing increasingly uncomfortable that my homicide detectives do not know all of the facts known to the FBI or USAO that could, if revealed to us, assist in furthering this murder investigation."

Davis has said he didn't know about Suiter's scheduled testimony until nearly a week after his death, and that he learned of the latest indictment of Jenkins at the same time as the media.

Jenkins is already in custody awaiting a January trial on criminal racketeering and fraud charges related to the corruption investigation. Since February, nine officers have been indicted in the case.

Davis said his department is continuing to run down leads in Suiter's killing and is not ruling out anything, including homicide by a still-unknown person, suicide or a conspiracy.

"We will follow the evidence where the evidence goes. ... We are not going to discount any possibility whatsoever," he said.

At the same time, Davis distinguished between "probabilities" and "possibilities," and repeatedly referred to Suiter's death as a "murder." He also said, as he had in the past, that physical evidence, including a garbled radio transmission from Suiter that ended with the sound of a gunshot, and the condition of the detective's clothing, indicates he was engaged in a struggle before he died.

Police have said Suiter and his partner were in a crime-ridden neighborhood seeking information involving a 2016 triple homicide when Suiter approached the suspicious man in a vacant lot, leading to a confrontation in which he was shot in the head. His partner can be seen on private surveillance video taking cover across the street, according to Davis.

With no arrests in the case, despite a $215,000 reward, and a churning rumor mill about the death and the investigation, Davis said he also sought to address public concerns.

"I understand the anxiety, and folks say, 'Something just doesn't jive here.' ... So, in the best interest of the integrity of the investigation, I just believe it's the right thing to do to ask the FBI to assume the lead," Davis said.