The love letters and poems were proof Williams didn't lie about Craig sexually harassing Macgregor, who suddenly resigned from her role as his press secretary two days before the 2014 election.
Time and time again the jury had heard from Craig his relationship with MacGregor was "a brother, sister relationship", McKnight told the jury.
"You should reject that - the letters speak for themselves."
Craig's legal team also had to prove the statements made by "this rich and powerful man" were honest opinion based on fact.
Williams however, believed he was acting in the best interests of Macgregor when he told other members of the party about the harassment and leaked it to right-wing blog Whale Oil.
"There really must be a stop to this person. He must be stopped from ruining so many lives. I suggest to you that there can be absolutely no doubt that Colin Craig was the author of his own misfortune and it does him little credit that he now somehow blames Jordan Williams for this," McKnight told the jury.
"Something needs to be done about this man and I leave that in your capable hands."
From the very outset, Williams wanted former Conservative Party leader gone and set about ousting him by spreading lies and stories he knew not to be true, Colin Craig's lawyer says.
In his closing statement in Craig's defamation trial in Auckland's High Court today, Stephen Mills QC said that when Craig sent out a leaflet and held a press conference claiming Williams and others spread false accusations about him he believed he was hitting back at "dirty politics".
In the fifth week of the trial, the jury heard Mills summarise the past three weeks of evidence and repeated his opening remarks that the case was not about the politician's former press secretary Rachel MacGregor.
"It's about Mr Williams and Mr Craig."
After MacGregor's shock resignation, she allegedly told Williams Craig had sexually harassed her through texts, cards, letters "and the now infamous" poem which included the line: "you are beautiful because you have the most perfect dot dot dot".
Against MacGregor's wishes and breaking her confidence, Williams passed the information on to members of the Conservative Party board and right-wing blog Whale Oil.
Mills told the jury there was evidence that showed Williams purposefully didn't seek to find out the truth.
One example was the relationship between MacGregor and Craig was not a "one-way traffic" and was more affectionate than she let on.
"All that Mr Williams had to do was look at that letter, it was right under his nose but he didn't want to read it."
Instead, he avoided seeking the truth so he could continue to spread the stories in his mission to oust Craig.
Mills said Craig distributed the pamphlet and held the press conference, because after the attacks he needed to defend his reputation and was standing up for what he thought was the right way to conduct politics in New Zealand.
His reputation had taken a hit from the "incredibly damaging" allegations, Mills said.
"If you are a politician and you are made a laughing stock, it's not survivable is it?"
But Craig didn't go away quietly.
"He fought back, which is how we got here," Mills told the court.
Mills told the jury it was up to them to decide whether Williams had "acted with honesty and integrity" while acting on the information MacGregor gave to him in confidence, and whether Craig believed the information he distributed was the truth and his honest opinion at the time.
"Whether they were ultimately right or wrong is not the test."
And if the jury decided that the answer is "yes, you think yes they're true - he [Williams] isn't trustworthy for example, then that's a defence."
Why is Colin Craig on trial?
The defamation trial unfolded after Craig's press secretary, Rachel MacGregor, resigned suddenly just 48 hours before the 2014 general election.
The resignation was high profile and there was much speculation about why she left.
Weeks later MacGregor turned to Williams for support, and told him she had made a complaint to the Human Rights Commission alleging that Craig had sexually harassed her.
She shared letters and poems the politician had sent her. Williams then revealed the details to other Conservative Party members.
When Craig found out, he publicly claimed Williams was part of a group of "culprits" determined to have him removed as party leader through a "campaign" of "false accusations".
Williams then filed defamation proceedings in the High Court, saying he did not lie about Craig.
The trial continues.
