Sicarius McGrath is a big guy. Muscled, shaven-headed and more than a little intimidating – everything you might expect of a Liverpool gangster.

But his days of roaming the streets of Anfield are over and now he helps steer vulnerable and deprived kids away from a life of gangland crime.

With convictions for violence and intimidation, he knows his subject and was an enlightening companion as together we toured the city’s estates, waiting for the jury verdicts in the Olivia Pratt-Korbel murder trial.

I drove, he talked. When he was setting up a gun factory and protection rackets he was known as Anthony Harrington.

At 7pm Sky News will broadcast a special programme: The murder of Olivia Pratt-Korbel

His adopted name Sicarius means “assassin”, but he didn’t go to a school that taught Latin. I did, but that isn’t the only difference between us.

“I used to put guns on the streets in massive volumes,” he told me, rather matter-of-factly.

“They are bought and paid for through drugs money. I felt responsibility 100% for the things that happened, whether someone was harmed as a result, but when you’re in that game you don’t give a s***. It’s profits over anything else.

“Decades ago there was a moral code, that you didn’t harm women, you didn’t harm kids. I’m not saying that little girl was shot intentionally, but those morals have gone out of the window.

“I was mixing in those circles and surroundings, so I’m a bit of a hypocrite to say now they are absolute scum, but I was once that scumbag.”

Read more: Thomas Cashman found guilty of murdering Olivia Pratt-Korbel

Although Merseyside Police had a key witness within a day or two of Olivia’s shooting, they struggled to find the direct evidence detectives always strive for.

There were no forensics, no eyewitnesses who could identify the killer and the two guns used have not been found.

I asked Mr McGrath how a close community deals with the conflict of outrage and the need for justice, set against loyalty and the fear of being labelled a grass.

“People are going to be reluctant, of course they are, depending on who commits the murder. If it’s established gang members people are going to be more reluctant. Everyone says there’s a code, no grassing, but criminals will grass each other up,” he said.

“It’s a question of what benefits them, if they can get a rival out of the way, bring police attention on them, but they’re not just gonna do it for charity.”

Gasps as Thomas Cashman found guilty on all charges – follow updates

What about the ordinary public – wouldn’t they be more scared of retribution for giving police information?

“It’s gonna be scary, they’re not really going to want to get involved, but when it’s a little girl the rule book goes out the window and you have to dig deep,” he said.

“People are more likely to engage with the police when it’s a young girl murdered and it’s up to the police to reassure them they are going to protect them.”

A month on from the shooting, after initial arrests but no charges, and with police still appealing for help, an anonymous businessman offered a remarkable £100,000 reward for information leading to the conviction of Olivia’s killer.

Lord Ashcroft, the founder of Crimestoppers, had also initially offered a £50,000 reward – but the anonymous donation prompted him to double his offer and, at £200,000 combined, it became the biggest ever reward.

At 7pm Sky News will broadcast a special programme: The murder of Olivia Pratt-Korbel

The other businessman, who did not want to be named for safety reasons, said: “When I heard that there was a seeming reluctance for people to come forward and testify, that’s what really got my back up.

“I thought, well, I’m going to try and do something about this. It was an amount that would make people sit up and make it as easy as possible for them to help catch the killer.”

The businessman’s family are from Merseyside and memories of his childhood in the area fuelled his desire for justice for Olivia.

“I understand people’s reluctance to speak out and I’ve thought about my own safety in putting up the reward. Like others, I had doubts and worries, but Crimestoppers assured me my identity would be protected. The bottom line is that this was horrific, the murder of a young girl. It doesn’t come much worse than that.”

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Mick Duthie, director of operations at Crimestoppers, said the reward had prompted “a phenomenal amount” of information from the public.

“I understand that in communities people don’t want to be seen as a grass or make themselves vulnerable, they don’t want to talk to the police, so the charity allows people to speak up anonymously,” he said.

“The community of Liverpool provided so much information. It wasn’t for us to decide how important it was. We took it and passed it on to Merseyside Police.”

As we drove through Dovecot, where Olivia was murdered, I asked Mr McGrath whether £200,000 was a life-changing amount for people in this community.

“For someone anywhere in the country it’s a life-changing amount of money,” he said.

“People are struggling to put their lights on and run their cookers. A reward of £200,000 is gonna benefit the vast majority of people, criminals and non-criminals.”

Sixteen years ago, schoolboy Rhys Jones, who was 11, was shot dead – caught in cross-fire – only a few miles from here.

I reported on it at the time and Mr McGrath was in prison, but we both remember the loud and widespread calls for change.

Mr McGrath said: “They always say that when a young person is stabbed or shot, they always say enough is enough, they’re going to take a stand but communities never do. It’s all just words.

“A couple of days or weeks later they go back to doing what they were doing. It’s only the families that are left suffering. Whoever shot Olivia, whoever’s convicted, his friends won’t stop talking to him because he shot a young girl.”

A blitz on organised crime and guns by Merseyside Police has driven down the number of firearms discharges to record low levels in the past couple of years.

There hadn’t been one reported in more than a year before last August. But then Olivia became the third gun murder victim in just a week. And there have been two more in the city since.