A massacre at Columbine High School. (2013). The History Channel website. Retrieved 12:33, June 18, 2013, from http://www.history.com/this-day-in-history/a-massacre-at-columbine-high-school.
A massacre at Columbine High School. [Internet]. 2013. The History Channel website. Available from: http://www.history.com/this-day-in-history/a-massacre-at-columbine-high-school [Accessed 18 Jun 2013].
“A massacre at Columbine High School.” 2013. The History Channel website. Jun 18 2013, 12:33 http://www.history.com/this-day-in-history/a-massacre-at-columbine-high-school.
“A massacre at Columbine High School,” The History Channel website, 2013, http://www.history.com/this-day-in-history/a-massacre-at-columbine-high-school [accessed Jun 18, 2013].
“A massacre at Columbine High School,” The History Channel website, http://www.history.com/this-day-in-history/a-massacre-at-columbine-high-school (accessed Jun 18, 2013).
A massacre at Columbine High School [Internet]. The History Channel website; 2013 [cited 2013 Jun 18] Available from: http://www.history.com/this-day-in-history/a-massacre-at-columbine-high-school.
A massacre at Columbine High School, http://www.history.com/this-day-in-history/a-massacre-at-columbine-high-school (last visited Jun 18, 2013).
A massacre at Columbine High School. The History Channel website. 2013. Available at: http://www.history.com/this-day-in-history/a-massacre-at-columbine-high-school. Accessed Jun 18, 2013.