Police in northern Greece on Tuesday were looking for the individual or group behind a flyer that encouraged hundreds of refugees and migrants to abandon a makeshift camp at Idomeni and attempt a perilous crossing into neighboring Former Yugoslav Republic of Macedonia (FYROM), CNN Greece reported on Tuesday.

According to the report, authorities were caught unawares on Monday when a group of a few hundred refugees and migrants – including dozens of children – suddenly left the Idomeni camp, defied Greek police trying to contain them and crossed a fast-moving river several kilometers away in order to reach a part of the FYROM border that was not fenced.

Police investigating what prompted this sudden exodus from the Idomeni camp reportedly discovered a pamphlet that was written in Arabic telling the Idomeni migrants to follow the particular route to the unguarded spot at a specified time.

It also reportedly said that “Germany is accepting migrants.”

Investigators believe the flyer may be the work of migrant smugglers, relief workers playing a shady role or activists who want to challenge closed-border policies, CNN Greece said.