In areas popular with the Arab community in Germany, Syrian refugees opposed to the Syrian regime have a growing concern.
Hundreds of militiamen supporting President Bashar al-Assad are believed to be taking advantage of the refugee crisis to gain access into Europe - arriving among those fleeing war.
Activists and human rights lawyers say the Assad loyalists, also known as shabiha, go undercover and supply the Assad regime with intelligence.
In Germany, activists are collaborating on social media to identify members of the shabiha and Assad forces by recording online profiles and current locations.
But they say the alleged criminals are deleting their online identities as they are being discovered.
Jikrkhouin Mulla Ahmed, a Syrian activist in Berlin who says he was imprisoned and tortured by the shabiha in Syria, says that when he sees people he is not sure about, he follows them to where they live and reports them to authorities.
"These people must be brought to justice for what they did," the told Al Jazeera. "This isn't just about me; more than 200,000 people have been made prisoners ... Many, many people were killed by the shabiha."
Several human rights lawyers in Europe acknowledge the threats posed by the infiltration of alleged criminals among Syrian refugees. The Syrian opposition in exile says also says it is trying to help.
The UN's Refugee Convention addresses criminals seeking asylum and similar provisions exist under EU asylum law.
The UN's Refugee Convention stipulates that those for whom there are serious reasons for considering that they have committed war crimes, crimes against humanity, or serious non-political crimes, should not qualify for refugee status.
Source: Al Jazeera