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But despite Andrew's shift having ended four hours earlier, the 28-year-old - who was on his way home when he heard about a group of "masked men with weapons" trying to break into a property - decided to attend one last job with his colleague.
It was testament to the kind of person Andrew was - kind, compassionate and always putting others first. It was one of the reasons he joined Thames Valley Police nine years earlier.
But it was also a decision that would cost Andrew his life.
Not long before the call came through, Henry Long, 19, Albert Bowers and Jessie Cole - both 18 - had stolen a £10,000 Honda quad bike from a property in Berkshire. They had hitched it to the back of a Seat Toledo getaway car and as they drove off into the night, they found themselves face-to-face with Andrew and his colleague, who were waiting in an unmarked car.
The driver of the getaway vehicle, Long, tried to manoeuvre around the police car, while passenger Cole attempted to unhitch the quad. But in a devastating twist, as PC Harper left the unmarked BMW and tried to apprehend Cole, he stepped into the vehicle's tow rope, and became lassoed to the getaway car as it sped off into the darkness for over a mile.
Despite all three teenagers claiming they were unaware that Andrew was attached to the vehicle, at the trial the prosecution argued that it would have been obvious. Andrew, who was 6ft, weighed 14 stone.
The court also heard that Long had been "deliberately swerving" as Andrew was dragged along the road "like a pendulum". After finally being freed, the newlywed died at the scene.
Many think that Long, Cole and Bowers' crime is deserving of the harshest of sentences, especially when considering the teenagers' lack of remorse throughout the trial.
In the midst of committing a theft, they killed a young man who had married his childhood sweetheart just weeks earlier. A man who was looking forward to his honeymoon in the Maldives the following month, to one day becoming a dad.
A man who, described by those who loved him as "a selfless hero" responded to a 999 call when he should have been safely home in bed with his new wife.
But at the trial in July, all three were acquitted of murder. Instead, the jury found Bowers and Cole guilty of manslaughter. Long had previously pleaded guilty to the same offence and was sentenced to 16 years.
Passengers Bowers and Cole were handed a sentence of 13 years and are now appealing both their verdict and sentence, while Lissie and Andrew's family have called for their sentences to be reviewed.
A fourth accomplice, Thomas King - who was charged with conspiring to steal a quad bike - was sentenced to two years imprisonment.
It was the moment when the verdict came in, Lissie tells Tyla, that she knew she had to take matters into her own hands. Three months on and the 29-year-old has set up Harper's Law, a campaign calling for a sentence of life imprisonment to be handed to those who kill a member of the emergency services.
It would mean anyone found guilty of killing a police officer, firefighter, nurse, doctor, prison officer or paramedic would automatically be jailed for life.
Lissie told us about the unbearable moment her husband's killers laughed and joked as if they were "at school" as they were acquitted of his murder, the "impossible grief" she now lives with and the fight for justice which gives her the energy to face each day.
"After everything, this process was supposed to bring justice for Andrew," Lissie said. "But when the verdict came in, I felt so let down. In that moment I knew there had to be another way, and something I could do.
"It's hard enough to go to court and hear all these awful things - the whole process is really an endurance. For them to treat it like they were in school or at a football match was really disrespectful.
"I don't have any control over the case, so with Harper's Law I'm really taking justice into my own hands. When this law is brought in, at least it will act as a deterrent for other criminals and hopefully it will help other families."
Lissie and Andrew - who were together for 12 years - often spoke about his job and the risks that came with it. Amidst the cop dramas and true crime docs that tend to glamorise what it means to be a member of the police, Lissie explains a lot of people don't realise the dangers.
It's something that has been brought to the public's attention twice now, within 15 months. Firstly, with Andrew's case and more recently, in the death of Sergeant Matt Ratana who was shot at Croydon Custody Centre last month.
"Andrew always wanted to be in the police; when we were first together it was either going to be that or joining the army. I know he would see the importance of this law, I know it's something he would want us to do," says Lissie.
"We always talked about the job and how risky it is. Unless you're in the job or you're with someone who is, you don't hear about that. It is hard and the police don't get the protection they should have.
"There's no real consequence of killing a member of the emergency services. It's a case of 'okay, we'll go to prison for a bit and then we'll carry on'. If Harper's Law was in place they would have to think twice.
"For Andrew's colleagues, I know he would be glad I'm trying to get this through for them."
Getting justice for Andrew is all consuming for Lissie, but she admits: "It helps me with the grief, it's so close to my heart. If it was anything else I'm not sure I would have the energy but this gives me a focus. I think you can get lost in dealing with grief in a closed in kind of way," she continues.
"Even just talking to other families who have been through a similar situation helps, and knowing that the general public are on board too, that keeps me going.
"Every day is a whirlwind of emotions and it does take a lot of my energy. While it is draining to keep talking about it and to meet with so many people, at the same time I feel it really helps me.
"Dealing with the grief feels impossible, I don't know how to, no one ever will and as humans we're just not very good at it. Whether this is the right way I don't know, it's a distraction I suppose. But I'm so passionate about it and I think that's only a good thing.
"I'm not a religious person but in a spiritual way, I like to think in my lowest moments Andrew is there with me."
Lissie has recently met with both the Home Secretary, Priti Patel and the Justice Secretary, Robert Buckland.
"[Buckland] has gone away to work to the legal side of it," she explains. "In the meantime, I've had meetings with the shadow cabinet as well to get some cross party support. I'm also speaking with MPs to tell them about Harper's Law and get support, as well as meeting people from the emergency services.
"People can help by spreading the word, signing the petition and if possible, contacting their local MP - this would really help the campaign move forward."
One thing that strikes us about Lissie is her constant use of the word "when" as opposed to "if". Not once does she think about the campaign as being unsuccessful - it's merely a case of when it happens - which she hopes will be within the next year.
"I'd like to say it will come in as soon as possible, but realistically probably a year at least. These things are so painfully slow. But I won't let it slip into the background."
You can sign the petition for Harper's Law here.
Featured Image Credit: PA
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