It was a seemingly cast-iron alibi.
Stephen McCullagh could not have murdered his pregnant girlfriend Natalie McNally because at the time of her death he was live streaming on YouTube.
But weeks later, in a police interview room, a detective pulled the rug from under his feet telling him that he knew McCullagh's carefully crafted alibi was false.
"That wasn't live," the detective challenged.
"What do you mean? You can see it play out on YouTube," replied McCullagh.
But it wasn't live, the police could prove it and from this moment the online content creator's high-stakes game of cat and mouse was up.
On Wednesday, McCullagh was sentenced for Natalie's murder - he will serve a minimum of 31 years before he can be considered for parole.
The 36-year-old, of Woodland Gardens in Lisburn, was found guilty murder after a five-week trial earlier this year.
Natalie was 15 weeks pregnant when she was killed in her Lurgan home in December 2022.
On 19 December 2022, McCullagh was arrested at the scene after apparently discovering her body. But he was released on the basis of his alibi.
Six weeks later cyber experts would blow that alibi to pieces.
They confirmed McCullagh had secretly pre-recorded a six-hour gaming stream that he then played out as live to give him cover to travel from Lisburn to Lurgan in disguise, kill his pregnant girlfriend and then get home before the stream ended.
That charade continued with texts asking about her wellbeing and the subsequent discovery of her body, followed by an emotional 999 call.
It was then that he immediately begun pointing the finger of blame at Natalie's ex-boyfriend.
"[McCullagh was] very confident of avoiding justice for this, and was playing the role of the victim across his friendship group, across the McNally family and the public in Lurgan," Police Service of Northern Ireland (PSNI) senior investigating officer Neil McGuinness said.
And he had been very close to getting away with murder.
Police had initially believed McCullagh's alibi because YouTube, the platform on which it had been broadcast, confirmed it had played out as a live broadcast.
He'd been 'de-suspected' as a result.
In the role of heartbroken boyfriend, McCullagh attended Natalie's wake, visited her grave and made a memorial video for a vigil in her honour.
All the while, he was secretly recording his interactions with the McNally family in the hope of garnering information about the investigation.
In the meantime, police were exploring other avenues, other suspects, hitting dead ends and trawling through mountains of CCTV.
With fears that an indiscriminate killer could be on the loose, pressure from the McNally family, the public and the press was building.
"Those were 15-hour days, for six weeks with no rest days," DCI McGuinness said.
"Most of my team didn't take any time off. They didn't see their families. They were there from morning to night.
"I met the McNally family very early on when I took over, and I made a commitment to them that I would literally work to exhaustion to try to bring them justice."
What eventually provided a breakthrough was a hunch.
"The task was to find someone getting onto a bus coming through Lurgan with a dark-coloured rucksack, because that's what we saw on the CCTV of the person leaving [Natalie's development]," McGuinness said.
"I remember it clear as day.
"It was Saturday afternoon and the officer phoned up and he almost apologetically said: 'This might be nothing, but I think I have something for you.'"
That officer had watched footage of a man with his face covered getting onto a Lurgan-bound bus in Dunmurry holding a green bag for life - he believed he could see a dark rucksack tucked inside.
That man was similar in stature to the man caught on CCTV at Natalie's development - similar in stature to Stephen McCullagh.
The PSNI had also been reviewing everything it knew about the investigation, including revisiting McCullagh's alibi with the help of its cyber unit.
"What they came up with was the use of a particular set of software, which semi-professional YouTubers would use to broadcast.
"They worked out a very peculiar feature of that system."
That related to the recording of background data.
That would continue on a live broadcast during the periods McCullagh was taking a break. But if the broadcast was pre-recorded, there would be no data for these periods.
To test this hypothesis investigators needed to seize McCullagh's computer, but given his media work, including as a part-time assistant audience editor at the Belfast Telegraph, this would require additional steps.
"That was a computer which was used in journalism, and there are protections for journalistic material," McGuinness said.
"I had a barrister and a solicitor with me in the police station overnight writing the warrant, and we went to court the next morning, secured the judge's permission to seize journalistic material, and then we went out and seized it."
McCullagh was rearrested on 31 January 2022.
During the interview process the cyber team were forensically examining his computer.
"The detective sergeant in the cyber-crime team called me up and said: 'Sit down, we've got him,'" McGuinness said.
This information was passed to detectives in the interview room and the screw was turned.
McCullagh was charged with murder, appearing at Lisburn Magistrate's Court on 2 February 2023.
Sitting in the public gallery were the McNally family.
Over the next three years, they'd attend dozens of court updates. Most only lasting moments. Many which served only to announce another delay.
New evidence, new reports, barrister strikes.
Delay, delay, delay.
They know better than anyone that waiting for justice is a frustrating experience.
This was a circumstantial case. There was no DNA, no eye-witnesses and no confession.
But there were dozens of strands that, according to Catherine Kierans of the Public Prosecution Service's Serious Crime Unit, painted the full picture – and it was her team's job to present this case to the court.
"The case was unprecedented in terms of the premeditation, the levels of deception and concealment, and really the extraordinary amount of planning to kill this young woman," she said.
"There were so many different strands of evidence, which all came together and fitted together to prove the case beyond any reasonable doubt.
"We have to remember the brutality of the murder itself. Then you've got all the other layers of cover up, deceit, the way that McCullagh ingratiated himself with the bereaved family, abused their trust, spied on them, manipulated them.
"You've got the framing of the ex-partner, but at the heart of this, you've got the brutal murder of a young woman and her baby."
As well as the CCTV and alibi evidence, Kierans believes some of the witness testimony the jury of six men and six women heard was crucial.
"The witnesses who came to court very courageously gave evidence, including McCullagh's former partner, who he had previously assaulted, and Natalie's former partner, who had been framed for this murder.
"I've never seen that happen before, where the person framed for the murder actually fronts up, comes to court and faces days of questioning.
"But that man was always very keen to assist the prosecution, which he did under intense pressure.
"There was no evidence that he was involved in this at all. All of the evidence pointed to McCullagh."
After taking three years to come to court, the murder trial against McCullagh lasted five weeks.
When the jury took just over two hours to reach a guilty verdict on the afternoon of 23 March, the pent-up emotion in Belfast's Court 13 was released.
When it was over, Natalie's family burst into cheers and applause.
They applauded the jury. They applauded the prosecutors and they applauded the police investigators.
After all the pain, disrespect and delays, justice had been served.
And although the McNally family have never voiced criticism, others have raised questions about what they perceive to be shortcomings in the early days of the investigation – particularly how and why McCullagh's alibi was initially accepted.
Neil McGuinness, who took over the investigation a few days in, said he doesn't believe the criticism is fair.
"Every decision that I make is made on the best available evidence at a point in time," he said.
"One of the first things that I did was have an officer contact YouTube in America to ascertain whether this footage was live streamed or not.
"YouTube sent us a very quick response back to say, yes, we confirmed that was live streamed, you know, and all appeared to be in order from their point of view."
He said that when the issue of McCullagh's alibi was later revisited, considerable efforts had to be undertaken just to seize the computer.
"That work couldn't have been done within the time periods we can hold people in custody [on the initial arrest]."
It is almost taken for granted in Northern Ireland that the gap between a suspect being charged and their eventual trial will be lengthy.
For Catherine Kierans, there is a balance in this argument.
She points out that fresh, important evidence, such as the discovery of a photograph of McCullagh wearing a hat and wig similar to the person of interest caught on CCTV was found only a short time before the trial.
She's also hopeful that in the long-term AI could be used to help police trawl through CCTV faster.
Catherine Kierans and Neil McGuinness never met Natalie McNally.
But securing justice for her was part of their daily lives for nearly three years.
"It can't be detached," McGuinness said.
"I wouldn't be human if I didn't focus on Natalie McNally, the person and her unborn baby.
"Part of our job is to give the voice to Natalie and part of our job is to bring justice for her and the life that didn't get a chance."
Kierans agrees.
"She had her whole life ahead of her so much promise, such an intelligent, loving young woman.
"We obviously became very attached to the McNally family and very involved with them, and the pressure to get justice for them."
