He allegedly crept into the room where the victim was sleeping with his girlfriend and smashed him at least twice in the head with a hammer, killing him instantly.
Ms Hawe only woke up when Tu allegedly snuck into the bed and tried to remove her clothes five hours later.
Tu had lived next door to the teenager since 2011 when she was 12-years-old and the court heard how he would shower her with gifts of alcohol and cigarettes.
But the Crown said his possessive personality was exposed when Ms Hawe started a relationship with Tangata Te Aho.
A witness, whose name is suppressed, told the court this morning that Tu offered him $50,000 to kill the man.
He said the defendant instructed him to sneak into Mr Te Aho's Onehunga home "like a ninja", slit his throat, put his body in the boot of his car and bring it to him.
Tu allegedly said he would then dispose of the body and give the prospective hitman the cash.
"I thought he was joking . . . I wasn't having a bar of it," he said.
"I told him it was a sick obsession. I played along for a while, to be honest. It gave me a good laugh."
The witness told the court he met Tu in 2014 in an Auckland strip club where he was sitting alone.
"He seemed like an alright chap at the time," he said.
Tu always had money, he said, which he claimed was from selling imported cigarettes to dairy owners.
The witness said his friend would splash out on methamphetamine and visits to brothels for both of them.
But he described Tu as "nutty".
His Facebook profile name was "Jesus Initiated" and the would-be hitman said he asked people for money on the social media site while claiming to be the son of God.
Their friendship eventually soured when Tu allegedly threatened to kill the man before they were coincidentally reunited in prison some months later in 2015.
"Several times he'd just stand there and yell that he was God," the witness said of his behaviour behind bars.
Yesterday the court heard that the force of the Tu's hammer blows was so strong that pieces of Mr Hawe-Wilson's skull were embedded in his brain.
"He didn't stand a chance. His death was so sudden he did not wake; in fact he barely moved," Ms Lummis said.
Tu later told police he killed Mr Hawe-Wilson to save his own life.
His lawyer Peter Tomlinson said the defence was one of insanity.
"There's no dispute that the defendant caused the death of Mr Hawe-Wilson, no dispute at all. But what the defence does say to you is that at the time he caused that death, he was so mentally impaired . . . he was incapable of knowing what he did was morally wrong," he said.
The trial, before Justice Christian Whata, is set down for three weeks.
