The Senior Engineer is a special Blue Suns mercenary located in the engine room of the MSV Strontium Mule. He is unique in being the only Blue Suns mercenary encountered by Commander Shepard with the ability to use tech attacks. He is killed during a firefight between Shepard and the squad when they reach the engine room of the ship.
The Senior Engineer is equipped with an M-300 Claymore heavy shotgun, which is armed with Incendiary Ammo. He is capable of dealing massive damage in close quarters. He can also deploy a Combat Drone.
One way to take out the Engineer is to Overload his shields and then use Kasumi's Shadow Strike to knock him off of his feet. Then he can be easily finished off with gunfire. Keeping your distance would also be a good idea as his shotgun won't be of any use at longer ranges.