The number of people in the Netherlands found guilty of human trafficking went down 25% last year, the NRC said on Monday.

In 2015, 139 people were jailed for human trafficking offences, around the same as in 2014. But last year, the total number of successful prosecutions fell to 103, the paper said, quoting figures from the Dutch law society.

Experts have differing views on why the number of cases has gone down. Tilburg University professor Conny Rijken said the police have focused more efforts on stemming the flow of refugees and tackling people smugglers instead. This, she says, has resulted in fewer human trafficking cases being brought before the courts.

Others say that the decline is ‘good news’ and shows the police are managing to tackle the trafficking gangs and their leaders.

However, Utrecht University criminology professor Dina Siegal told the paper it is becoming harder to prove human trafficking. It can be a ‘very subtle’ offence, she said, in which victims accept what is an unfair deal with the trafficker and do not, therefore, consider themselves victims.

The maximum penalty for human trafficking was increased to 12 years in 2012 but that the average sentence was 585 days.  Just five suspects last year were jailed for more than 1,500 days and almost a quarter of suspects are eventually found not guilty, the paper said.

Many of the victims end up in prostitution.