Jerry Dyer told reporters the crime appeared to be "solely based on race".
On one music video titled "U Gone Need Me: "Tru Story Kori" in which he discusses racism and the "liberation of his people", he says: "... on a mission for the liberation of my people.
Dyer said investigators allowed Muhammad to speak on the phone to his mother, who was crying.
Muhammad is then believed to have walked on through downtown Fresno, shooting at another white person and missing, sparing two women in a auto who were Latina, and then fatally shooting two more white men, aged 37 and 58, all within less than two minutes before he was taken into custody by police.
The man had just gone shopping at a Catholic Charities building when he was gunned down.
The suspect then fled and hid on a gas station roof.
He also allegedly pointed the gun at three Hispanic women - a woman, her adult daughter and her 4-year-old granddaughter - who heard the gunshots and got into their vehicle, which had trouble starting.
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Police had been looking for Muhammad in the death of the guard, 25-year-old Carl Williams.
Muhammad also has a criminal history in Sacramento dating back to 1997 when he was arrested for making criminal threats.
Witnesses said they saw a man carrying a large handgun, who reloaded it several times between shots. According to the authorities, he told the police that he hates Caucasian people. He's also suspected in the shooting death of a white security guard last week. Friday morning, he watched police officers investigate the crime scene and by evening he was in a ravine, where he told police he conducted voodoo rituals for three days.
The guard, Carl Williams, 25, was shot multiple times.
Muhammad told detectives that he is Muslim but hadn't been to mosque in 20 years and prays to numerous gods, Dyer said. Three people were killed and none are believed to have previously known Muhammad.
At one point he shot at a auto, but when he saw there were two Hispanic females inside, he stopped his attack.
The Fresno police chief also told reporters that the suspect's Facebook page included posts that expressed hate for white people.
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All four of the men killed on Tuesday were white, as was the security guard and the other man Mohammad shot at but missed.
A Catholic Charities spokesperson said there does not appear to be any connection between the shooter and Catholic Charities, the Fresno Bee reported. The suspect, Kori Ali Muhammad, 39, is black.
Maria Praise told CNN she ran inside and locked the doors when she heard the sound of gunfire.
Muhammad faces four counts of murder and two of attempted murder, according to Dyer.
She said there has been an outpouring of support for Catholic Charities and that there was a long line of clients awaiting services as normal early this morning outside the charity at 149 N Fulton St.
He was deemed mentally unfit to stand trial in 2005 after a grand jury indicted him on cocaine and firearm possession charges.
He claimed insanity and his lawyer requested a psychiatric examination, saying Muhammad "appeared eccentric with some freaky beliefs". He also said he'd had "at least two prior mental health hospitalizations". His attorney said that Muhammad had "paranoia" and thought the justice system and his defense attorney were conspiring against him, court papers said.
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Dyer believes that race was the motivation behind the killings on Tuesday as well as Williams.