May 3 is World Press Freedom Day, the UN-gazetted date that focuses global attention on defending media producers from attacks – on their lives and their independence – and pays tribute to the many journalists who've been killed or imprisoned in the course of their work.

This year's celebration marks the 250th anniversary of the world's first freedom of information law, established to cover the modern territories of Sweden and Finland. It's fitting, then, that Finland's capital Helsinki is hosting UNESCO's annual global World Press Freedom Day conference this week. Less fitting is the Finnish Government's attempt to intrude into a global journalistic investigation.

Illustration: Simon Bosch.

The creeping threat to investigative journalism posed by the erosion of journalistic source protection internationally is in the spotlight in Helsinki as journalists at Finnish public broadcaster YLE come under pressure from the government to hand over a cache of documents from the Panama Papers.

YLE analysed the files as one of the global media houses collaborating on the biggest act of cross-border investigative journalism in history.