IT was a five year investigation that took detectives across Europe to track down a gang exploiting vulnerable women to satisfy their own greed.

For lead investigator Detective Constable Kirsty Lee there is one word to describe what was uncovered during Operation Synapses - “heartbreaking”.

The complex nature of the investigation becomes clear as officers reveal the details of an operation crossing three countries, six UK police forces and involving four languages.

Officers say they were first tipped off to a crime gang working in Govanhill in 2014, prompting an inquiry that would see Police Scotland’s dedicated national human trafficking unit work closely with other UK forces, Europol, the cross-border crime unit Eurojust, and colleagues in the Slovak police force.

READ MORE: Govanhill trafficking gang was family who sold women like cattle

Not all the victims involved remained in Glasgow, meaning police had to trace witnesses in Slovakia, Birmingham and London.

Ms Lee said: “Anybody who can sell a human being like they are selling a car, I think is really disgusting.

“It was actually quite heartbreaking.”

Her colleague Detective Inspector Steven McMillan added: “Most of our cases we try not to get involved and attached but for some it’s really difficult and this is probably one of them.”

While the investigation began in flats in Govanhill, officers were soon travelling to Slovakia to work with colleagues there.

It became clear that the Glasgow traffickers were part of a network with links across the UK, including South Yorkshire, the Midlands and Bedfordshire, and in the Eastern European country.

READ MORE: Govanhill community: Horror but no surprise as four guilty of trafficking

A core inquiry team of eight was supported by a large contingent of additional officers working closely with colleagues in Slovakia.

Last year, after five years of evidence gathering, five accused went on trial at Glasgow Sheriff Court.

During evidence, however, one witness talked for the first time of being raped and the trial was deserted before being moved to the High Court.

For prosecutor Kath Harper, this strengthened the case as new electronic evidence was introduced.

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The Advocate Depute said: “This really had a High Court feel to it, it is the trafficking of women.

“In the interim, unknown to everybody, we got phone evidence in which text and Skype messages make it very plain that Anil and Gombar and possibly Rastislav and Jana were definitely involved with [a victim].

“It also strengthened the case against Wagle.

“The fact that human beings are being sold is shocking. Literally sold 10 minutes from this court. Sold, exploited and treated like chattels.”

Lawyers in Slovakia and Scotland decided to proceed by prosecuting those living in Scotland here and those living in Slovakia in that country.

READ MORE: Govanhill trafficking trial: Where are the men who bought the victims?

Ms Harper had hoped the women victims would come to Glasgow to give evidence but they did not want to return here after their ordeals.

This meant the prosecutor was seeing witnesses for the first time in court as they appeared by video link from Slovakia and spoke with the aid of interpreters.

“The distance involved, the fact you have no relationship with them, and the interpretation is quite challenging,” she said.

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“There were a lot of hurdles. I found taking evidence quite hard.

“Trafficking trials are always going to have these hurdles. There are layers of complication to these cases.

“But the Slovakians have been tremendous because really we were at their mercy to provide witnesses and the video link.”

A further six members of the gang are on trial in Slovakia.

This caused issues when those accused were called to give evidence before Glasgow’s High Court.

Under Slovakian law they could exercise a right not to testify, in case of incriminating themselves, and the Scottish court was unable to compel them.

In the end, this additional evidence was not needed as the jury returned a guilty verdict, vindicating the efforts of police and prosecutors - and hopefully bringing closure to the victims.

READ MORE: Govanhill trafficking gang: How did victims fall prey to twisted traffickers?

Detective Superintendent Fil Capaldi said: “Human trafficking is an insidious crime often unseen, often unrecognised, and has no respect for international borders.

“It has a devastating impact on the victims.

“In this case the crime group exploited vulnerable women using violence, threats and false promises to trade them and advertise human beings to be bought and sold like commodities.

“This was all for the purposes of greed and financial gain without any thought for the suffering these women had to endure.”