COPENHAGEN: Four men went on trial on Thursday accused of helping the gunman behind twin attacks on a Copenhagen synagogue and a free speech event last year that left two people dead.

The trial, being guarded by about a dozen heavily armed police, comes with Europe still on high alert over fears of militant violence following two bloody attacks in Paris in 2015.

Prosecutor Bo Bjerregaard accused the four defendants of trying to “destabilize or destroy Denmark’s basic political, constitutional, economic or societal structures.” The killer, 22-year-old Omar El-Hussein, opened fire on Feb. 14 last year outside a cultural center where the speakers included Swedish artist Lars Vilks.

A 55-year-old filmmaker, Finn Norgaard, died and three police officers were injured. Later that night, the Dane of Palestinian origin fired six shots outside the city’s main synagogue, killing security guard Dan Uzan, 37, and injuring two more policemen.