Police in Belgium were looking for four men who used a train’s public address system to threaten to blow up the vehicle near Antwerp unless Jewish passengers step off.

The suspects took control of the public address system on Wednesday afternoon between Antwerp and Mechelen, the city that Nazis and their collaborators used as an internment and dispatch station for Jews whom they sent to be murdered in Poland.

Security personnel on the train failed to locate the perpetrators, according to Michael Freilich, a Belgian-Jewish lawmaker who has looked into and filed parliamentary questions about the incident to the Transportation Ministry.

Freilich asked the ministry to explain why the perpetrators were not caught, how they gained access to the address system and what can be done to prevent a recurrence.

The ministry has two weeks to respond.