The paranoid Bourke Street driver spoke of mowing down innocent strangers hours before the massacre, but frantic calls and texts to a detective investigating him went unanswered.
Detective Senior Constable Murray Gentner was hunting James Gargasoulas and called the offender's friend late on the night of January 19, 2017, warning he was "out of control".
The friend, who cannot be named for legal reasons, told an inquest on Tuesday the detective asked that he be called if they came into contact with him and that his phone would be on all night.
Gargasoulas then showed up at the friend's home in the early hours of January 20, paranoid and with bloodied clothes.
Feeling threatened, the friend repeatedly tried to phone the detective to no avail.
They also texted him, saying: "He's scarey and cooked Help".
In another message they wrote: "James is in a Commodore off his nana ... possibly just bashed his brother .... call me ASAP."
They said Gargasoulas also threatened: "I'm going to do something drastic, take everyone out, they can suffer the consequences, watch me, you'll see me tonight on the news, the police have stopped me before but they ain't gonna get me this time, I'll make you believe me."
The friend said they had no doubt Gargasoulas was on a mission and would carry out the drastic threat.
The friend said the offender also commented on random people on the street, saying: "I'm just going to mow them down".
"I told him not to do that," the friend said.
The friend finally spoke to Det Sen Const Gentner on the morning of January 20. "I asked him why didn't you answer your phone, you said it'd be on all night."
The friend said the detective didn't say to also call triple-zero if needed.
However, Det Sen Const Gentner has told the inquest the friend knew to call triple-zero in an emergency.
Under cross examination from Det Sen Const Gentner's lawyer, the friend agreed there was nothing to stop them calling the emergency number.
Later that day on January 20, Gargasoulas ran down people in the CBD, killing six pedestrians in Bourke Street and harming dozens more.
Detective Sergeant David Barry tailed Gargasoulas across several suburbs just before the tragedy, and said the help of the state surveillance unit was sought twice but no one was available.
He also said he did not seek help from the special operations group, the force's highly trained tactical experts, as the situation did not meet their criteria, given there was no threat against a particular person.
Det Sgt Barry agreed police were "essentially" left without proper support in their bid to stop Gargasoulas.
They relied on Det Sen Const Murray Gentner's rapport with the offender on the phone and via messages to try and get him to surrender peacefully as police followed him before his deadly rampage.
Gargasoulas, who suffers paranoid schizophrenia, was jailed in February for at least 46 years.
© AAP 2019