BERLIN (Reuters) - German police arrested three people on Wednesday in a nationwide operation to crack down on a gang accused of trafficking migrants into Germany in trucks last year.

The police said they arrested a Turk, aged 44, a 37-year old Pole and a Bulgarian, 53, in raids on seven properties in Berlin, Bremen, North Rhine-Westphalia and Saxony.

Investigators believe the traffickers smuggled at least 160 migrants into Germany in the summer and autumn of 2017, hiding some of them in trucks behind goods and pallets, police said.

Immigration remains a politically charged issue in Germany after Chancellor Angela Merkel’s decision to open the doors to more than one million migrants and refugees in 2015 and 2016.

The traffickers demanded 8,000 euros ($9,950) per migrant and brought most of them into Germany via Poland or the Czech Republic after coming north from the Balkans, police said.

“The investigations in this case show once again that unscrupulous traffickers are only concerned about profit,” Joerg Baumbach, federal police head in Pirna, said in a statement.

“They do not care about the well-being of those who entrust themselves to them for a lot of money.”