It’s hardly a secret but nothing sells books or TV drama like murder.

But details of real-life killings are equally as compelling.

So much so that the most senior Crown Prosecution Service (CPS) prosecutor in the Midlands admits: “I prefer murder cases to any others. I just wonder what makes someone who was a decent human being suddenly snap.

“What turns someone into a killer?”

Peter Grieves-Smith, 44, smiles and asks: “Are all individuals born bad or born good and become bad?”

The veteran barrister, who has become the first and only Principal Crown Advocate across four CPS regions in the Midlands, hasn’t the time for quasi-philosophical quandaries.

Peter moved into the role in December 2008 after a stint prosecuting organised crime for the Serious Organised Crime Agency.

Right now, he’s working on five murders and seven attempted murders. It’s no wonder then that he’s at his city centre desk at 7am; works four hours in his study most week nights and sometimes puts in an extra 24 hours at weekends.

So with years of experience both as a prosecutor and defence barrister, does he believe there’s a potential to kill lurking in all of us?

“I think you have to look at it on a person by person basis,” he says. “The other side of the coin is if you’ve got someone who appeared to the world to be wonderful and then they suddenly snap and kill someone.

“There’s a little niggle in the back of my mind, maybe there was something there but nobody saw it. You just don’t know. I don’t want to judge but I do wonder what has made someone who appears very decent snap.”

Peter took a big pay cut to join the CPS while his appointment has saved the public purse a tidy fortune. Previously, the CPS employed highly-paid barristers in private practice to prosecute their biggest cases. That still happens but now on an increasingly lesser scale.

Now the man most often seen prosecuting CPS West Midlands’ most serious, complex or sensitive cases is impeccably-dressed Peter. And he’s yet to turn down a case.

Notable recent cases have included that of Brazilian national Gabryela Passos, who used a bucket of petrol to cause horrific life-threatening burns to Ricardo da Silva; a Birmingham man accused of killing his father with a machete and a Staffordshire woman lawyer who stole almost £100,000 from vulnerable clients so she could treat herself to breast reduction surgery.

But far from minding the incredible workload, he clearly thrives on it.

“Two months ago I began reading a murder case at 11.30pm.

“I couldn’t put it down.” He finally did at 2am. “I was reading a mixture of statements and interviews.

“I do worry about missing something. By the time we’ve finished a case I’ll have read, for example, transcripts of a phone call, 10 or 12 times.

“You just keep working and working and working. It’s never tedious. We’re trying to get it 100 per cent right and so much is at stake.

“It’s about preparing and presenting the evidence in a fair and accurate way.

“It’s a team effort. I work closely with police officers, different people at the CPS, all of us are reading a case. The aim is you never miss something. I think on the whole it pays off.”

Perhaps unlike some veteran cops, there’s no gung-ho approach to winning cases.

He explains: “When I was about six months as a tenant (start of his career) I said to a lady QC in my chambers ‘I’m going to prosecute a shoplifting trial and this looks a bit of a winner’.

“About 20 minutes later I emerged from a lecture about why we don’t aim to win cases, that’s not why we’re here.

“Prosecutors are here to present evidence, winning is the wrong way to approach a case because if you start to look at the concept of winning it’s just all wrong.”

Peter thought for a moment and said: “There’s a phrase that prosecution win no victories and suffer no defeats. That’s the basis upon which we prosecute. The second you introduce winning then you lose your independence.

“I don’t get three points every time I get a conviction. What matters is doing the job properly and fairly.”

And yet despite his professional, measured, ‘lawyer-like’ approach to cases, he admits he’s been deeply affected by cases. Recently it was the plight of Birmingham transvestite Ricardo da Silva.

Peter prosecuted his attacker, Gabryela Passos at the end of last year. She got 20 years. The Brazilian national set light to Mr da Silva after a row over a missing handbag and laptop, at his flat in the Digbeth area of Birmingham in December 2008.

Her 25-year-old victim – who was initially given less than a 50 per cent chance of survival – spent more than three months in hospital, undergoing 16 operations, and still faces further surgery after suffering burns to 70 per cent of his body.

Peter said: “I admire him so much because faced with the injuries he has at his age he could have stayed at home and not fought in the way he has fought, in the way he came to court and behaved with courage and dignity.”

Other haunting cases include that of David Brown, a disturbed Black Country man who broke into his elderly neighbours’ home, tied up the couple and subjected them to unimaginable torture. He came close to slicing through their wrists.

“He had gone next door with a serrated knife and injured his elderly neighbours, very slowly, very deliberately. If you were to give medals to victims they’d have got one. They were an astonishing couple.

“To hear their police interviews played in court was one of the most moving experiences ever in my career. They never once said ‘Oh, the agony, oh, it was such pain’. For them it was very factual. The fact they weren’t complaining was just incredible.”

One case above all others stands out in his mind. It rendered him on the brink of crying in open court.

It was the prosecution of a man who had raped his ‘girlfriend’.

He recalls: “She had been sold and worked as a prostitute across Europe, having gone from Romania, down to Albania, across Albania to Italy and worked her way through Italy, acquiring languages along the way.

“Then she had been bought by the defendant, I can’t remember how much for. He took her to London, raped her and beat her. She eventually escaped. It was just a horrific thing to do to somebody. You forgot she was 16. She’d been through more difficulties in life at 16 than almost any of us. The sheer horror of the allegation was unbelievable.

“I met her. She was just a very nice girl and was coping with life and starting afresh. There was a moment when she was giving evidence in court, she was behind screens and she described the violence she had got from the defendant.

“She started crying and I nearly did. The emotion in court was just so astonishing and yet despite that, you have to maintain your objectivity and not get angry. It was very very difficult. At that point I suspect I wasn’t the only person close to tears.”

I ask him if some cases are a foregone conclusion from the outset. On paper, yes, he says. But everything can change when someone’s giving evidence.

Four years ago he prosecuted the case of a man who’d been accused of indecently assaulting the daughter of a friend.

When Peter got to court the evidence was so compelling he reckoned the defendant might plead guilty.

He met the victim who was eight years old and lovely. She played with his wig. Then when the jury was out the child admitted she had made it all up.

“I was horrified. She had admitted it to her grandmother who was with her at court. I think the grandmother knew her better than anybody and picked something up. I think the grandmother thought, ‘This isn’t right’.

“The defendant had been in custody for four or five months. So that’s why you try not to go into a case thinking this is overwhelming, you’ve got to have a healthy amount of doubt.

“The doubt keeps you sharp, the doubt makes sure you’re being fair to everybody.”

The police and charging lawyers had believed the girl in that case.

The CPS is not allowed to prosecute cases if there’s not a reasonable chance of conviction.

Does he believe that clever, cunning defendants can put on such a courtroom act as to fool a jury into acquitting them? “I think people’s personalities come out in court, whether it be the defendant or a witness. I remember prosecuting a guy years ago who was accused of indecently assaulting his step-daughter.

“On the face of it it was quite a strong case. I asked what he thought of his step-daughter and his answer showed to me very clearly how much he loved her.

“Suddenly his personality came out and he hadn’t come over very well until then. Suddenly you could just tell the love for his daughter and he was acquitted.”

There have been difficult nuts to crack though. Like the immigration judge who had formerly been a High Court judge in Kenya. Peter successfully prosecuted him for fraud. “That was hard work, battling someone who was very bright.”

He much prefers prosecuting to defending. “You’re building a case, you start with a great big pile of evidence and you’ve got to put that together so that it makes sense to you and a jury.

“And as you go through it you’re trying to understand it through somebody else’s perspective. You’re trying to see what may be wrong with a case so you can plug a gap. And trying to look at it from a defendant’s pointy of view. It’s like building a house and you’re trying to make sure everything fits together, is accurate and correct.

“Defending is totally different. When you’re defending you’re trying to knock the house down.”

He admits he has prosecuted suspects who may have been innocent.

“There was a guy who’d been an Army captain, he’d served in Iraq, Bosnia, you name it. Everybody said what a great guy he was and he was meant to have hit somebody in a pub.

“I just didn’t believe it. If he’s not snapped or lost his temper in any of those countries why’s he suddenly snapped in a pub? It just didn’t sound very believable to me. He was acquitted.”

He must get depressed. He says: “Oh God, you read some cases and think, how could anybody do this? How could anybody think this was a good idea? You think about how the victim has suffered. Many, many cases I read I feel so sorry for what has happened.

“And I know that I can’t say anything that is going to make their loss, their sadness better.

“All I can do is hope that by doing my job as professionally as I can it will be part of the process of helping whoever has suffered.”

For Peter, the most intense, dramatic emotions of the job come with the finale of the trial – as the courtroom awaits the return of the jury.

He says: “From the viewpoint of the defendant it’s never going to get any more dramatic than that. When the jury comes back he might be walking out of court in ten minutes. He might be starting a life sentence.

“When a verdict is delivered in a murder case it is an astonishing moment. You start to tremble. I think with virtually every verdict in every case of any significance the pulse rate starts.

“Sometimes people in the court chatter but they’re not really listening. They’re just trying to fill the silence.”

Then the door to the jury rooms opens.