Camp Speicher massacre

On 12 June 2014, the Islamic State killed at least 1,566 Shia Iraqi Air Force cadets in an attack on Camp Speicher in Tikrit. At the time of the attack there were between 4,000 and 11,000 unarmed cadets in the camp. Alleged ISIS fighters singled out Shia and non-Muslim cadets from Sunni ones and executed them. The Iraqi government blamed the massacre on both ISIS and members from the Arab Socialist Ba'ath Party – Iraq Region. (Wikipedia)

Arrests in Finland
Two Iraqi men were arrested in Finland in December for "terrorist murder". An online propaganda video is claimed to show the twin brothers killing 11 bound prisoners.
 * In Finnish: KRP:llä tutkinnassa 11 terroristisessa tarkoituksessa tehtyä murhaa - Iltalehti, December 10, 2015
 * Two detained in Finland over ISIS executions in Tikrit - YLE News, December 10, 2015
 * Finland detains two Iraqis suspected of featuring in Islamic State massacre video - Adam Taylor. Washington Post, December 10, 2015
 * Finland detains Iraqi twins over IS massacre in Tikrit - BBC News, December 10, 2015
 * Finnish Police Arrest Iraqi Twins Linked to ISIS Massacre in 2014 - DAN BILEFSKY, The New York Times, December 10, 2015
 * Daesh executioners suspects detained in Finland - New Europe, December 10, 2015
 * Joukkomurhasta epäillyt kaksoset herättivät huomiota Forssassa – väitetään kuunnelleen Isis-lauluja - Ilta-Sanomat, December 11, 2015  (Interview in English)
 * FINLAND: TWIN BROTHERS ARRESTED BY FINNISH POLICE FOR MASSACRE INVOLVEMENT SANG ISIS SONGS, HATED SHIITES - Tundra Tabloids, December 11, 2015