Scotland's failure to successfully prosecute anyone for people trafficking is "startling", a senior police officer has admitted.
Dep Ch Con Gordon Meldrum said there were at least 10 criminal gangs smuggling people into Scotland.
But no-one has ever been convicted of the offence, despite several successful prosecutions elsewhere in the UK.
Mr Meldrum was giving evidence to Holyrood's equal opportunities committee.
The committee is carrying out an inquiry into migration and trafficking in Scotland.
Mr Meldrum said he did not know why there had never been a successful prosecution for people trafficking in Scotland, and said there was a "startling" difference in the conviction rates between Scotland and England.
He told committee members that the Scottish Crime and Drug Enforcement Agency had last year, for the first time, attempted to map the scale of serious organised crime in Scotland.
Its study found that in June of last year there were a minimum of 367 serious organised crime groups, with a total of about 4,066 named members, either active in Scotland, or whose activities directly impacted on Scotland.
Of these, at least 10 groups were thought to be actively involved in people smuggling, Mr Meldrum, whose portfolio with the Association of Chief Police Officers includes trafficking, said.
But he added: "In Scotland, to the best of my knowledge, we don't have a conviction for human trafficking. We had one case which was brought to court previously but was abandoned. My understanding is it was abandoned due to a lack of evidence, essentially.
"That does compare and contrast with the experience south of the border, where there have been a number of successful prosecutions in different part of the country.
"Why is there such a difference? I honestly don't know the answer to this."
He said that the legislation on human trafficking was "slightly different" elsewhere in the UK, but added: "Simply because the legislation is different, frankly, shouldn't mean there is such a marked difference from north to south.
"Certainly from speaking to colleagues at the Crown, their view is there is no debar in terms of the legislation in Scotland to a successful prosecution."
A major UK-wide crackdown on people trafficking under the codename Pentameter 2, which was launched in 2007, saw police reports to the Crown for offences such as keeping brothels, but no-one was reported for human trafficking, Mr Meldrum said.
This was partly because a number of victims who were recovered during the operation vanished shortly afterwards, he explained.
Mr Meldrum added: "The other issue for us is actually to get victims to speak up, and not only to speak up in the first instance but to last the duration of any investigation and subsequent court case."
The committee was also told that no-one knows for sure the scale of human trafficking into Scotland.
Lorraine Cook, of Cosla's strategic migration partnership, described human trafficking as a "hidden crime" while the trafficking of children was "even more so hidden".
An ongoing pilot project by Glasgow City Council had identified eight cases of children being trafficked into the city - but officials believe these are only the tip of the iceberg, Ms Cook said.