The number of activists killed exceeded 13,000 as the following quote from Barbara Harff, professor of political science emerita at the U.S. Naval Academy in Annapolis, Maryland showed:
“And on the democratic side, Sri Lanka is one clear case of a democratic regime that in 1989–90 authorized military squads to track down and summarily execute members and suspected supporters of the JVP (Peoples Liberation Party), which had begun its second rebellion that threatened to overthrow the state. Between 13,000 and 30,000 were killed in this politicide...”
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^Harff, Barbara (2017). "Chapter 12: The Comparative Analysis of Mass Atrocities and Genocide". In Gleditsch, N. (ed.). R.J. Rummel: An Assessment of His Many Contributions. Springer. pp. 111–120. doi:10.1007/978-3-319-54463-2_12. ISBN978-3-319-54462-5.