(CNN) -- Police officers who unleashed a hail of gunfire that killed a homeless Michigan man wielding a knife will not face criminal charges, prosecutors said Wednesday.
Saginaw County Prosecutor Mike Thomas told reporters that investigators had reviewed police reports, several pieces of evidence -- including audio recordings of phone calls made to police -- and interviewed several witnesses at the scene.
"Criminal charges aren't warranted," said Thomas, noting 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," he said. Hall's family said that he had a history of mental illness.
The 49-year-old man had been arguing with officers in a parking lot next to a shuttered Chinese restaurant when he was shot multiple times by police, 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 prior to the shooting in which she complained that he had been rude and aggressive, and had refused to pay for a coffee and other items.
The woman also said Hall had 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 threatened the officer with a 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 the female officer's voice, which was 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 officer added. "He's going to kill somebody."
Thomas said six of the eight police officers opened fire as Hall approached. The officers had been equipped with stun guns, though they "aren't 100% effective," he added.
The officers fired 46 rounds, striking Hall 11 times, according to Thomas.
Investigators also showed video of the incident, captured by a dashboard camera inside a police cruiser at the scene.
The eight officers, as well as a police dog, had formed a semi-circle around Hall, who did not appear to back down during the confrontation, according to the video.
"They didn't shoot him right away at the beginning," said Thomas. "They tried to look for non-lethal options here."
Thomas said "there is a need for greater (police) training," as well as a need for more access to non-lethal weapons.
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, who said her son was mentally ill, has plans to speak Monday at a "town hall type meeting" organized by Concerned Citizens of Saginaw at a local church.
Jewel Hall said last month that she and her attorney were conducting a separate investigation. They are requesting access to additional documents as well as the autopsy report.
"I have good days and bad days," she said Wednesday. "Today is not a good day for me."
In a statement released through her attorney, Hall said she was "disappointed in the prosecutor's report finding that the actions of the six Saginaw police officers who so brutally shot and killed my son, Milton Hall, were justified."
"If there is any benefit to come from Milton's tragic death, we would hope that it would be to raise awareness of the challenges confronting the Saginaw Police Department and Saginaw elected officials," she said in the statement. "The challenges are serious, systemic, wide-ranging and deeply rooted."
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, 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.
CNN's Sheila Steffen and Jake Carpenter contributed to this report