When you're dealing with victims of crime it can sometimes be what you don't know that's most disturbing.
How many more of them are out there?
What are the signs that we missed?
Are we spotting others before it's too late?
Nobody could have failed to be affected by the harrowing story of a 10-year-old girl trafficked from her home in Pakistan to Manchester.
Profoundly deaf, unable to speak, she was kept as a slave, repeatedly abused and valued only for the benefits her captors could claim on her behalf.
A few days ago those individuals were jailed for a total of 18 years by a judge who while noting their appalling behaviour quite rightly referenced the "extreme vulnerability" of their victim.
Trafficking, slavery, grooming, call it what you will, there is a common theme emerging, and that is the profile of the victims.
My charity and many others have just marked Antislavery Day.
Ministers were obviously aware of the significance of this date too announcing tougher penalties for those convicted of trafficking offences.
It's encouraging that the state is reacting to what is an emerging issue for the authorities, the criminal justice system and society as a whole.
But it's vital that we don't just up our game once the offenders have been convicted - by then the damage to the victims has already been done.
We know the case of the 10-year-old girl is not isolated.
What we don't know is how many times and where it is being replicated.
Often isolated, with no friends or family, victims are afraid of presenting themselves to the authorities for fear of being punished themselves. For them, any kind of help or support must seem beyond their reach. And so they remain unidentified, with nowhere to turn.
If we're walking down a street in the most normal of communities, how do we really know what is happening beneath the surface?
The Global Slavery Index recently found that at least 880,000 people are forced to work in slave labour conditions across Europe, including 270,000 victims of sexual exploitation. It is shocking that this seems to be a conservative estimate.
Modern day slavery - human trafficking - doesn't just happen across international boundaries of course.
It was on show in all its horror earlier this year with the systematic sexual exploitation by a gang in Oxfordshire of vulnerable girls who were supported at court by Victim Support's Witness Service.
My first thought though is that while bringing these people to justice is so important - equally so is reaching out to those trafficking victims who need us.
In Bristol, our Victim Support team is supporting partners in a unique anti-trafficking partnership with the police, the council and anti-trafficking charity Unseen. We are there to help victims who want to escape, but are too afraid to approach the authorities. It is already proving to be very successful.
Hearing the distressing stories of the people we have supported brings home just how important this kind of partnership working is.
One of them told our volunteers how she was trafficked from Eastern Europe after being promised a good job - which of course never materialised. Forced into labour, with awful living conditions - being fed once a day, if at all.
This is a horrific, yet sadly familiar story these victims have to tell and a painful reminder that crime prevention is always better than a cure.
The third sector undoubtedly has a unique and vital role here as an independent, impartial, 'first step' on the way out for these very vulnerable people.
There is also the question of a consistent response for trafficking victims - wherever they find themselves in the UK. If the girls in the recent Oxford case had had access to the pathways on offer in Bristol, I wonder, would they have been identified and given the help they so desperately needed a lot sooner?
But the first step for all organisations which might come into contact with these vulnerable people is to learn how to better recognise those who might be victim to this terrible crime.
Only when we know the signs can we hope to help these people who so desperately need us.
And only then will we know just how many people that is.