Wounding with intent to cause grievous bodily harm carries with it potential imprisonment of up to 14 years, and had Sem-Cheyne been found guilty, he would have almost certainly been staring down the barrel of a lengthy stay behind bars, counsel Anne Stevens QC said.
But after just one day, the Crown agreed to offer no further evidence and Judge John Macdonald dismissed the charge.
Sem-Cheyne was vindicated, he was not guilty, the nightmare was over for him and his family.
But it was not.
"There's that relief but it's still playing on my mind, how it really got to that point," he told the Otago Daily Times.
"Am I really free? I'm still doubting myself."
His mother Sophear described the past two years as a nightmare and blasted those who handled the case.
"The police did a s... job. The Crown did a s... job," she said.
"I expect better. These are people we trust."
She was adamant there was never enough evidence to charge her son; they would take their concerns to the Independent Police Conduct Authority (IPCA) and would make an application with the court for costs — a bid for some financial recompense for what he had been through.
August 18, 2018 was a typical Saturday night.
Two of Sem-Cheyne's friends were celebrating their 21st birthdays and held a joint party at a Woodhaugh flat.
There was a DJ outside under a gazebo, furniture had been moved aside for a makeshift dance-floor, there was talking and drinking.
Then Henry Cooper, Joshua Henderson and their friend arrived.
The mood quickly soured as a man with a longstanding grudge against Henderson grabbed him by the throat.
As Cooper tried to intervene, Sem-Cheyne stepped in.
The pair scuffled briefly before another man took control, punching Cooper and removing him from the party.
The victim, who had some boxing experience, told the court at this week's trial that he was unhurt after the melee.
It felt like he been through some "light sparring", he said.
However, it was not over.
As he walked down the driveway, others followed; there was the sound of breaking glass and footsteps behind him, he recalled.
Then — nothing.
He regained consciousness minutes later, "staring up at the night sky".
Sem-Cheyne said he had been with his girlfriend, well away from the violence, when he heard a loud bang.
He believed it was the sound of Cooper slamming into a car after being hit in the right side of the head from behind.
The Crown's version at the start of the trial, however, was that the blow was delivered by the defendant, who went on to strike the unconscious victim as he lay on the ground.
That was almost solely on the back of the accounts of three women, who said they turned up at the party at that critical moment.
They were interviewed more than two months after the incident — much later than many witnesses — and all told police it was Sem-Cheyne.
None of them were asked to identify him from a photo montage and the ODT understands two of them were interviewed by police by phone.
When Sem-Cheyne read their witness statements in 2019, he said his "heart dropped".
One of them was the then girlfriend of a man who chased Henderson down the road that night and assaulted him.
Sem-Cheyne believes it was him or his brother — both given diversion for punching Henderson — who was responsible for the attack on Cooper, and Stevens put it plainly for the jury in her opening statement on Monday.
"[The women] are lying to protect their friend," she said.
In the witness box, the trio's stories changed slightly, particularly the key witness who said she was now unsure what or who she saw.
There was no way a jury could convict Sem-Cheyne, so he never heard a verdict.
The judge's dismissal had the same effect.
Not guilty.
The early acquittal meant he never got to raise some of the issues he otherwise would have.
How could he have hit Cooper in the right side of the head from behind when he had longstanding ligament damage in his right hand and could barely form a fist?
Why would he have sat with Cooper after the fracas had ended and apologised only for the scrap inside the house if he had committed the second attack?
After being barred from contact since the charge was laid, the pair came face to face after the trial fell over.
"He shook my hand and said he was sorry I had to go through that, and messaged me later that day," Sem-Cheyne said.
"It was a big weight off both of our shoulders."
Sem-Cheyne was spoken to by police a week or so after the incident and was surprised when officers turned up at his home in December 2018, asking for his cellphone.
He willingly gave it to them and it was soon returned.
Then, in April 2019, he was charged.
Sem-Cheyne, who had no criminal record, was stunned, his mother was "horrified", and so the ordeal began.
He had to take time off his job, working as a full-time support worker for people who had suffered brain injuries, at a private residential facility.
He started smoking more, drinking more, his weight seesawed and he stopped sleeping, as the pressure took its toll.
"I didn't want to leave the house, I'd just be so tired and stressed," Sem-Cheyne said.
His mother said it was "heartbreaking" seeing her boy go through the turmoil of not knowing his fate.
At the trial's abrupt ending this week, the relief they felt was quickly replaced by anger that they had been forced to endure a near two-year hell.
Sem-Cheyne hoped the police would continue to investigate and eventually charge the true culprit, and she urged them to charge the three female witnesses with making a false statement.
Police refused to comment on the case as it had been raised with the IPCA, but said they would "consider any new information ... should it come to light".
Sem-Cheyne had read about people being accused of crimes they did not commit, innocent parties on trial, but he never imagined himself standing in the dock, framed.
He had been in the wrong place at the wrong time.
And if it happened to him it could happen to anyone, his mother said.
If the investigating officers and the Crown had scrutinised those witness statements, there was no way her son should have been charged, she said.
"The way we were treated was disgusting," she said.
"We want answers."
