'Murdered on camera - the video that shocked two juries'

The jury was shown a graphic video of Yostin Mosquera (L) stabbing Albert Alfonso to death

Warning: This article contains details that some may find distressing, including violence and descriptions of a sexual nature.

I have reported on numerous court cases covering some horrific murders and abuse.

But nothing could prepare me or the jury for what we would see and hear during the trial of Yostin Mosquera.

On Monday he was found guilty of the double murder of Albert Alfonso, 62, and Paul Longworth, 71, in their London flat.

As a journalist working on the case I knew Mosquera was accused of killing and dismembering Mr Alfonso and Mr Longworth - after all, I had been in Bristol when the grim discovery was made of their bodies in two suitcases at the Clifton Suspension Bridge.

We had also found out Mosquera and Mr Alfonso originally met because they both made extreme sex videos which were posted online - so we knew this was going to be a distressing story to cover for all involved.

Yostin Mosquera sat in the dock with an interpreter as the jury watched him kill Albert Alfonso

Now that a verdict has been delivered, we can reveal that two trials were started into the murders.

One at the Old Bailey started in May, but collapsed due to problems identifying accurate timings on some of the computer evidence.

The trial was moved to Woolwich Crown Court and started all over again at the end of June.

I bring up the fact that there were two trials, because two trials means two juries.

In both trials, the jury were asked to watch an extremely harrowing video of Mosquera and Mr Alfonso having sex before Mr Alfonso was brutally stabbed to death on 8 July last year.

Each time the judge, Mr Justice Bennathan, warned them that they were about to watch a distressing bit of footage, filmed on four different cameras set up in Mr Alfonso's bedroom.

But he said it was necessary to do so to help bring justice.

The trial was heard at Woolwich Crown Court

You could see there was a knife which Mosquera had concealed on a table under some cloth.

What then began with an extreme sex act between Mosquera and Mr Alfonso very quickly turned into an unexpected attack.

Albert was wearing a white swimming cap and a black leather eye mask when Mosquera attacked him with the knife. The eye mask depriving him of one of his senses.

It was so tense in court. There was total silence.

It was such a traumatic watch, it was first played without any sound.

The next day, the sound was broadcast, which made it so much worse.

As Mosquera was carrying out the murder, you could hear him ask Mr Alfonso if he "liked it".

Then you hear Mr Alfonso take his last breath.

Police from both forces investigating the case, Avon and Somerset Police and the Metropolitan Police, said they were profoundly affected by the video.

One officer at the Met said a colleague went "white as a sheet" after viewing it, and officers told me despite being used to watching many grim things, it was "by far one of the worst things they had ever seen in all their careers".

But for a jury - made up of everyday people, picked entirely at random – they did not ask to be part of this trial, or choose a career path where they would be exposed to such graphic content.

It makes you wonder how they coped with seeing these images.

At the end of the day during the first trial, one jury member handed the judge a note saying they could not bear to watch it again and asked to be discharged.

The jury was now down from 12 to 11 people.

Recoiled in his seat

When the first trial collapsed my first thought was about that poor jury that had been made to sit through all that footage for nothing.

During the retrial, I was in a fortunate position that I did not have to watch the murder, instead I chose to watch the second jury.

Knowing what they were seeing, I was not surprised by their reaction.

One man physically lurched back in his seat, recoiling from what he was seeing, another woman wearing a scarf tightly wrapped it around her mouth as if trying to protect herself.

The prosecution told the jurors they blurred out as much as they could.

The video was played to them three times in the first three days.

Mosquera had earlier killed Paul Longworth, by hitting him over the head with a hammer

I was covering the trial, along with Adam Crowther, tracking its twists and turns for the BBC Sounds podcast Bodies in the Suitcases.

Myself and Adam made different decisions on whether to watch the video.

Adam did not look away.

He later told me it was probably the most shocking thing he has ever, and would ever, see in his life.

While the cameras captured Mr Alfonso being murdered, his ex-partner and best friend, Mr Longworth, had already been placed in the base of a divan bed in a room next door.

He had been dead for hours after being fatally attacked with a hammer by Mosquera.

'Serious demand on jury'

Through the trial we heard about Mr Alfonso's predilection for extreme sex.

This included accounts of domination, degrading sex acts and a world of online videos that are made, posted online and bought and sold – many aspects of which would be seen as disturbing by most.

Mosquera had claimed it was Mr Alfonso who had killed Mr Longworth – and it was following this that he had feared for his own life and killed Mr Alfonso after a loss of control.

But of everyone we spoke to who knew Mr Alfonso, no-one described him as dangerous.

Ultimately the jury would agree and it took them just over five hours to find Mosquera guilty of both murders.

Speaking to the jurors, Mr Justice Bennathan acknowledged the "serious demands" that had been placed on them "in this case more than most".

"They were terrible, brutal events and to read about it is a dreadful thing, but to see it is really shocking," he said.

Jurors are now eligible to six counselling sessions if they have had to sit through distressing cases.

But even with help, they will likely never be able to unsee what they had to watch.