“I’ve seen many tears shed throughout this from professionals, not just within policing.”

Those are the words of the man who had the heavy responsibility of leading the investigation into the Southport stabbing attack that killed Alice da Silva Aguiar, nine; seven-year-old Elsie Dot Stancombe and Bebe King, six.

It was approaching 13:00 BST on 29 July when Det Ch Insp Jason Pye heard the news.

The vastly experienced detective was in Liverpool Crown Court dealing with another case when he got a phone call about what had just unfolded at a Taylor Swift-themed dance workshop in Hart Street.

One hour earlier, Axel Rudakubana had moved through the Hart Space dance studio systematically stabbing child after child.

Rudakubana ended his rampage meekly, dropping his kitchen knife and surrounding to the police without a word.

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But by then, three children were dead, eight children and two adults were seriously injured and 15 other children were left with unimaginable trauma.

Det Ch Insp Pye said it was a “long six months” until the moment, on Monday, when Rudakubana surprised everyone by changing his pleas to guilty on what should have been the first day of his trial.

For much of that time, and in the full glare of the international media, his investigation team and the wider Merseyside Police force had seen and heard the most harrowing evidence of their collective careers.

“Yes this is our job, we put our hand up to do it,” he said.

“We never expect to wake up in the morning and come to something like this but neither did any of those 26 children or their families or the adults as well.”

Acknowledging the toll of the case, Det Ch Insp Pye added: “It is difficult.

“It’s difficult for people who constantly see some of the details, and who have had to read through it on a constant basis, not just within policing…

“But it’s the families and getting justice that keeps us going day-by-day.”

The exceptionally harrowing nature of Rudakubana’s crimes has meant several officers in the force have had to take sick leave.

“I know that there are some police officers who are still struggling and are off work at the moment because of what they’ve come across and what they’ve seen,” he said.

The horrific details of Rudakubana’s crimes were only one part of the immense strain placed on Merseyside Police last summer.

Less than 48 hours after he had been taken to Copy Lane police station, the appalling details of the crimes – coupled with misinformation about the killer’s identity and background – sparked violence on the streets.

A vigil on the evening after the murders turned into what the force’s Chief Constable, Serena Kennedy, described as “one of the worst nights of my career”.

More than 100 officers and police staff injured during outbreaks of violence, first in Southport, then in Liverpool City Centre and in Walton.

Some of those called to battle with rioters hurling missiles and damaging police vehicles had also been called to the aftermath of the massacre on 29 July.

For the detectives laser-focused on unravelling the truth of what happened, the mayhem on the streets was absolutely baffling.

Det Ch Insp Pye said: “It was very, very fast moving until we got him charged.

“He was arrested round about 12 o’clock on the Monday [29 July] and with an extension I could have 72 hours maximum, so we had to charge him by just after midnight on the Wednesday.

“To come in and see those riots within the community where these three little girls had lost their lives and everybody else had been impacted in the way that they had was really distasteful for us, it was difficult to understand why it was happening, and it had a real impact on the families as well.”

For Det Ch Insp Pye, the task of the 80-strong team of detectives was to tune out the unfolding catastrophe and carry on with the task at hand.

There was no painstaking investigative work needed to get the killer identified and into custody – that was the “easy bit” – according to Det Ch Insp Pye.

“The difficult part is what I class as all this noise that’s been around it,” he said.

“We have to assess the noise, we have to see whether we need to bring it in evidentially, so that’s what’s been difficult, that’s what’s created the complex investigation not the actual evidence itself.

“I’ve tried, if I’m honest, to stay away from social media and stay away from the conspiracy theories but we have had to be aware of it as an investigation team in case there was anything that we would have to bring into the investigation.”

The most important task is now done -Rudakubana has admitted every offence against him and will more than likely spend the rest of his life in prison.

For Det Ch Insp Pye, now is the time most distressing parts of their careers could manifest itself.

“Now that we’ve [got justice] and now that things have steadied down a little bit – that might be the time that we need – to reflect and just consider the welfare of all of our officers,” he said.

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