A turian military unit, the name "Kexaknus" meaning something akin to 'Their Death.'
While certainly difficult to find, information on the group isn't actually classified. Kexaknus was designed to work alongside hastatim forces as a sort of 'hunter-killer' unit; adept at finding insurgents, militant separatists and other such undesirables ingrained within a populace, and eliminating them. They were a cut above the average hastatim soldier.
Founded in 2163, the group spent two years on a form of trial-run, engaging in low-level operations throughout Turian Hierarchy space. In 2165 the unit was sent to Solregit, a rather infamous separatist hotspot, and would be deployed there repeatedly after this in order to try and crush the 'Sundowner' faction. The unit was greatly successful, but suffered nearly 85% casualties rate: preemptively going after insurgents in their home territories is dangerous work. When the movement was finally broken in 2175, Kexaknus spent the next year searching for Sundowners who had gone underground, but was eventually redeployed on the grounds of 'effective resource application' when only a few fugitives were found.
Following this, they were sent to the edges of the Terminus Systems, where they operated for three years until a incident on Dreonas in 2179. The unit was hunting a major terrorist in the colony's primary settlement, and while this fugitive was attempting to escape in a shuttle and make for the system's mass relay, he was shot down. In broad daylight, the shuttle crashed into an apartment complex in the heart of the city, killing seventy people.
To compensate for the backlash, Kexaknus was shelved, the unit disbanded.
More people have at least heard the name "Kexaknus" now, after the case of Aractis Amborix (The Hidden), a Kexaknan assassin with an extreme nationalist streak who "died offscreen" prior to the season premiere of The Life Egregious, in a tragic whining accident (he was quickly forgotten by the rest of the team). Possibly the earliest sign of the particular style of humour the show would be infamous for.