Citadel Security is a volunteer police service answering to the Citadel
Council. The 200,000 constables of C-Sec are responsible for maintaining
public order in the densely populated Citadel. They also provide pirate
suppression, customs enforcements, and search-and-rescue- throughout the
Citadel cluster.
C-Sec has six divisions:

ENFORCEMENT - Uniformed officers who patrol the Citadel and respond to
emergencies.

INVESTIGATION - Detectives who puzzle out the truth behind crimes and bring
perpetrators to justice.

CUSTOMS - Screen the thousands of passengers and cargo containers that pass
through the Citadel's ports every day.

NETWORK - Deals with "cybercrimes" like identify and copyright theft, hacking
and viral attacks, and illegal artificial intelligence.

SPECIAL RESPONSE - Deals with hostage situations, bombs, and heavily armed
criminals. In the unlikely event that attackers board the Citadel, they are
also the front line of defense, armored with military grade equipment.

PATROL - Naval arm, with ships stationed throughout the Citadel cluster.
Unlike the other divisions, they are rarely seen at the Citadel, nor do they
stay in one place long.

Joining C-Sec is prestigious; applications must be sponsored by a Citadel
Councilor or the ambassador of an associate Council race. Generally,
applicants have many years of distinguished service in the military or police
forces of their nations, but an inexperienced applicant with demonstrable
talent will be fairly considered.

C-Sec and Spectres are often at odds. May C-Sec members, notably the current
Executor Venari Pallin, believe that allowing Specters to be 'above the law'
is a dangerous practice, the actions of Saren Arterius lend credence to this
position. The Spectres, in turn, are aggravated within C-Sec's dedication to
procedure and due process hampers their investigations.

Would some humans still be a part of C-Sec, even though the Alliance seceded from Citadel space?

Even though the Allliance Seceded there are still humans that live and work in the citadel.

So yea. :D

The Alliance didn't secede from the Citadel though. You're thinking of a human faction, the Terra Firma. Systems Alliance is still a part of the citadel.

Oh.

o_o

welll.

I feel stupid...

Don't. This is a plot that doesn't come from the game itself, it was brought around in the RP after page and page of story you aren't exactly expected to have read through ;)

Still, I should have known the difference between the Terra Firma and Earth, which is where I got mixed up... But what's done is done.