You can pick up this quest immediately after gaining intel from Vehn Terev (whichever way you go about doing it) during the quest “Hunting the Archon”. Immediately after leaving Outcast Headquarters, head south through Kadara Port to find a group of people standing around a murdered Angara near Kralla’s Song. Simply approaching is enough to start the quest, but scan the corpse to get some background on the murder spree in Kadara Port and the presumed suspect. SAM will then suggest that you find Vidal, who might have more information.
Ride the lift down to Kadara Slums and enter Tartarus - the bar that takes up a significant portion of the buildings to the west. Make your way upstairs and enter a private room to the west to find Reyes Vidal, who is all too quick to discount the Charlatan as your culprit, after which he’ll guide you to the conclusion that the Roekaar may be behind the murders. This would take their extreme xenophobia against aliens to cannibalistic levels - killing their own to punish (and discourage) Milky Way sympathizers. Vidal seems to have taken it upon himself to do more research into this matter than one would expect, but to gain more answers than he can immediately provide, the Pathfinder - or more specifically, their AI - is needed.
This ends the quest “Murder in Kadara Port” and begins “A People Divided”.