Human trafficking gangs are guilty of crimes against humanity for their brutal treatment of vulnerable Rohingya refugees trying to flee to Thailand and Malaysia, say human rights groups who released a harrowing new investigation on Wednesday.

The 121-page report, Sold Like Fish, by the Human Rights Commission of Malaysia and Fortify Rights documents the horrific abuse of thousands of Rohingya, who were starved, raped and murdered at sea by traffickers who then enslaved survivors in camps and extorted them for more money.

The crimes were committed between 2012 and 2015 when 170,000 mainly Rohingya refugees trying to flee persecution in Burma were hoarded onto overcrowded boats by greedy trafficking syndicates who made an estimated $50m-100m a year from their trade in people.

The study, based on 270 interviews with survivors and officials, documents mass graves and internment camps along the Thai-Malaysia border, and comes ahead of a Malaysian-government appointed Royal Commission of Inquiry report in June into the dumping of dead trafficking victims in Perlis State in 2015.