1. abc7chicago.com. (4. Oktober 2016). Reports of clowns approaching students spread to Chicago. http://abc7chicago.com/news/reports-of-clowns-approaching-students-spread-to-chicago/1538828/.
2. abc15.com. (30. Oktober 2016). Scottsdale police: Suspicious item inside vehicle rendered safe, no explosive material found. http://www.abc15.com/news/region-northeast-valley/scottsdale/scottsdale-police-investigating-possible-bomb-threat.
3. America’s Waterway Watch, U.S. Coast Guard. (no date). Where should I look for „suspicious activity?“. http://americaswaterwaywatch.uscg.mil/Suspicious_Activity.html.
4. Barrera, D. (2015). Bomb threats and reports of suspicious items in the Philippines: Spatial and temporal patterns. Security Journal, 30(3), 665–685. https://doi.org/10.1057/sj.2015.1.
5. Belcher, M. (11. Oktober 2016). Suspicious item found on X-ray screening at DIA, police responding. Denver7 News TheDenverChannel.com. http://www.thedenverchannel.com/news/local-news/suspicious-item-found-on-x-ray-screening-at-dia-police-responding.