Prosecutors say the review was needed because police weren't going to investigate itself
Saginaw County Prosecutor Mike Thomas said six police officers opened fire as Hall approached
Hall had been arguing with officers when he was shot multiple times, in full view of passing motorists
(CNN) -- Police officers who fatally shot a homeless Michigan man wielding a knife will not face criminal charges, prosecutors said Wednesday.
Saginaw County Prosecutor Mike Thomas told reporters on Wednesday that investigators reviewed police reports, several pieces of evidence -- including audio recordings of phone calls made to police -- and interviewed several witnesses at the scene.
Prosecutors determined that the officers had not acted with criminal intent on July 1 when they opened fire on Milton Hall.
The 10-week investigation was necessary because "the Saginaw Police Department was not going to investigate itself," Thomas said.
Hall's family said he had a history of mental illness.
Hall had been arguing with officers in a parking lot next to a shuttered Chinese restaurant when he was shot multiple times, in full view of passing motorists and while he was holding a knife.
Prosecutors played an audio recording of a call made to police by a woman at a nearby mini mart in which she complained that he had been rude and aggressive, and had refused to pay for items that he removed from the store prior to the shooting.
The woman said Hall spit on someone inside the store, according to the recording.
A female police officer responded to the call and radioed in for backup when she encountered Hall, who was being aggressive and had threatened her with the knife, according to Thomas.
Investigators said Hall refused to drop the weapon, despite police orders to relinquish the knife and came within a few feet of the officers.
"He's coming at us every time we exit the vehicle," according to a female officer's voice broadcast to reporters during Wednesday's press conference. "He wants us to shoot him."
"We can't let him get out of this area," the woman added. "He's going to kill somebody."
Thomas said six police officers opened fire with their guns as Hall approached. The officers had also been equipped with stun guns, though they "aren't 100% effective," he added.
Thomas said earlier at the onset of the investigation that the squad of police confronting Hall opened fire "because apparently, at this point in time, he was threatening to assault police."
Hall's cousin, Mike Washington, told CNN in August that Hall had been jailed for minor offenses such as vagrancy in the past, but, "he was not violent."
Hall's mother said her son was mentally ill. She told CNN on Wednesday that her lawyer plans to release a statement in response to the investigation's findings.
"I have good days and bad days," said the Albuquerque, New Mexico resident. "Today is not a good day for me."
The shooting occurred in a parking lot on West Genessee Avenue, a busy commercial strip on the north side of Saginaw.
In a video purchased by CNN, shot by a motorist from across the street, the 49-year-old Hall is seen arguing with a half-dozen officers. For more than three minutes, he walks back and forth, and at one time appears to crouch in a "karate stance," according to the man who captured the scene.
Multiple shots are heard in the video.