The Warzone 2 Cartel Investigation is one of the new Redacted faction missions for DMZ that was introduced in season three. While it's not quite as tricky as killing the Scavenger and finding his calling cards, it can be tough to locate the cartel on a map as expansive as Al Mazrah.
To complete this DMZ mission, you're going to have to find them and steal some Large Contraband Packages before escaping to extraction with the loot. So, here's where to find the cartel on the map, and where to locate the packages you can steal.
Where to find the cartel and Large Contraband Packages
The Cartel Investigation mission requires you to find the new gang in Al Mazrah, kill five of their foot soldiers, and steal two Large Contraband Packages before extraction. You can find the cartel in the Hafid Port area in the west of the map, towards the south-east end by the UAV tower, where they'll be hanging out in the open by the warehouse buildings. They're actually a lot better to kill than the regular Al Mazrah soldiers as they aren't armoured, and carry better weapons to loot like M16s and LMGs.
Once you've killed five of them, you need to grab two Large Contraband Packages. The best place to find these random items is on shelves and tables inside the nearby port buildings—they basically look like big cardboard boxes with blue corners. It might take a little while as you rummage through rooms, but you'll find a few lying around. After you've grabbed two of them, simply head to extraction to complete the faction mission.
It's worth noting that I encountered a bug with this mission where I got downed and changed teams, and it didn't count me extracting the packages despite having them in my inventory, so maybe play it safe if you don't want to have to do it again.