My partner leaves the interview room telling him he's going to be questioned about a homicide,

and he removes a notebook from his pants pocket, like a small notebook where you can just keep

in your back pocket. And he tears out a piece of paper from that notebook and eats it. And then

he thumbs a couple pages up and tears out another piece of paper and he eats it and chews and

and swallows both of those pieces of paper and then sits down.

I'm Scott Weinberger, investigative journalist and former deputy sheriff.

I'm Anasiga Nikolaazi, former New York City homicide prosecutor and host of investigation discoveries true conviction.

And this is Anatomy of Murphy.

When we talk about the phrase, a perfect crime, it's a pretty simple concept.

In the perfect crime, the criminal gets away what they've done. But as we know, very few things in life are actually perfect.

And in the scenario where someone thinks they've figured out all the angles and can commit crime without being caught, well, fortunately, that's usually not the case.

Because there's almost always another angle, something not planned for, something overlooked, a slip of the tongue that could turn everything upside down for the perpetrator.

And today's case will go down all of those roads.

On the afternoon of March 24, 2016, a 911 call was placed by 34-year-old Cornelius Green.

He reported finding his girlfriend, 30-year-old Jocelyn Peters, dead in her home.

Mark Beondolino, now a 23-year veteran with the St. Louis Metropolitan Police Department,

responded to the call. It was his first year as a homicide detective.

We're the day shift crew. It was towards the end of the shift.

I think it was between 3.30 and 4 when the call came in to the location, which was 42-36 West Pine, for a shooting with the victim remaining on the scene. I was up as the lead investigator and my partner and I were up.

Mark arrived at Jocelyn Peters apartment complex, which was located in the central west end of the city.

It was a very quiet, very nice neighborhood. I'd say low crime as far as violent crime.

I think there were 16 total units in this very nice, very secure, multi-unit apartment complex.

...