Sometimes it can start with an advert or even a text message, offering work, education, a new life and fresh hope.
Sometimes it can end tragically, perhaps in a container lorry at a foreign port far away from home.
Small fortunes, often borrowed, are handed over to crime gangs by desperate people to arrange for them to be illegally smuggled across borders, according to criminologist Craig Barlow, who has worked on a number of human trafficking cases.
Other times people are smuggled by gangs with the specific intention for them to be exploited; women sexually, men for labour, children for begging.
Often people being smuggled are simply tricked and end up being trafficked and exploited all the same, a life of “debt bondage” to pay the smugglers off.
Instead of a fresh start in a new country they find themselves in a world of deceit, coercion, abduction and violence from ruthless crime gangs.
Mr Barlow, an expert in human trafficking cases, said: “That’s the bottom line, whether they were complicit with their travel, by travelling illegally or they were deceived into travelling, these were 39 people who were just looking to better their circumstances.
“It’s a heartbreaking tragedy.
“Imagine yourself in a situation, you may have already been subject to violence by people controlling you, you may be forced into the back of a vehicle or if compliant you are told, ‘It’s going to be a bit uncomfortable, but just sit tight’.
“Two hours pass, three hours pass, you can’t open it from the inside, you are depending on traffickers to let you out or someone else to find you.
“What’s difficult for members of the public to understand is the degree of control and coercion.”
The latest figures from the National Referral Mechanism (NRM) gives a summary of the number of potential victims of modern slavery.
The figures show for the second quarter of 2019, between April 1 and June 30, 2,320 potential victims of modern slavery, of 84 different nationalities, were referred to the NRM; an 8% increase from the previous quarter and a 40% increase from the same quarter in 2018.
In 2014 the number of referrals were around 600 per quarter.
Mr Barlow said: “Whatever country people are coming from, there may be any number of reasons, it may be they are looking for work opportunities, or education opportunities.
“What can sometimes occur in countries of origin, you find people looking for work, seen an offer in a newspaper or advert or text message and say, ‘OK, that looks like a good opportunity.’
“Approached by an agent, gives me the terms and maybe they charge me an upfront fee or a work placement will be sorted out, just give us your passport.
“Once they have travel documents they have control of the victim, it may be the victim does not realise this is a bogus operation.”
Routes taken by both smugglers and traffickers can be “extremely convoluted” with people passing through a number of different countries, stops-offs along the way and people being kept in warehouses for weeks at a time.
Victims sometimes do not even know which country they are in if they are rescued by the authorities.
Gangs behind trafficking can vary in size and sophistication, with the nature of their crime business determining who they target.
Organised crime is also “agile” and communication and travel is much easier, easier for criminals to communicate, to launder money and to move people.
Mr Barlow said: “For the crime gangs there are huge returns with comparatively little risk because detecting them is quite hard and also what you find is that often with professional gangs that that’s not the only criminal activity they are involved in.
“People when they are exploited can be exploited in a whole number of ways.
“I worked on a case where a victim was handed over in payment for a debt, she was being effectively handed over for a Mercedes car.”
Exactly why the 39 people found dead in Essex, whether smuggled or trafficked, how they came to be in that container and for how long, is now the subject of a massive police inquiry, which is likely to take some time.
Mr Barlow added: “The investigation and also evidence, is very difficult.
“There are clearly no witnesses to it, it’s going to be a difficult process, working back from Essex to the source country, identifying these people and working out how they came to be there.”