Four years of terror in Europe have claimed 244 lives

A ceremony pays tribute to a French police officer and his partner, who were killed June 13 by a man claiming allegiance to the Islamic State group.

A woman reads messages written on the ground at a makeshift memorial at Place de la Bourse following attacks on March 22 in Brussels.

Crime scene investigators at Leytonstone tube station in east London collect evidence after a man was seriously injured on Dec. 5 by a knife-wielding attacker who reportedly shouted, “This is for Syria.”

Paris residents take part in a moment of silence under the Eiffel Tower in observance of those who died during the terrorist attacks on Nov. 13.

Police walk on a platform next to a Thalys train of French national railway operator SNCF in Arras after a gunman opened fire on a train traveling from Amsterdam to Paris in August 2015.

French police secure the entrance of the Air Products company near Lyon, France, where an attacker carrying an Islamist flag killed one person and injured several others at a gas factory in June 2015.

Armed French police patrol north of Paris after officers shot a man who was attempting to gain access to a Paris police station while brandishing a knife in January.

A Jewish boy stands with flowers in front of the Jewish Museum in Brussels, two days after a shooting attack killed an Israeli tourist couple in May 2014.

Police investigating the stabbing of a French soldier in Paris arrest a suspect described as an adherent of “radical Islam” in May 2013.

During a commemoration ceremony at Burgas Airport, Israeli Tourism Minister Stas Misezhnikov pays respects to the five Israeli victims of a suicide blast that targeted a bus of Israeli tourists in July 2012.

A woman lays flowers at the site of a blast near a school in Brindisi, Italy. A 16-year-old girl died after a powerful bomb exploded outside her school in May 2012. Seven others were injured, one critically.

Paratroopers carry the coffin of a French paratrooper who was shot to death in Toulouse, France, in March 2012. The funeral procession at Montauban Cathedral passed by the paratrooper’s pregnant fiancee, right.