Megapol police officers are responsible for enforcing law and order on the city. Since they are also well armed they would be of a great help during Battlescape but unfortunately they will never be present when X-COM is reacting to alien alerts at their buildings.
The only way to meet (and fight) officers in combat is if Megapol has turned hostile towards X-COM or if X-COM is conducting deliberate raids on their buildings.
Megapol officers are among the best-armed human combatants (starting Tech Level 3) and have slightly higher Accuracy scores and Armour (note that they do not wear Megapol Armor) than other organizations' troops. However, they are also more vulnerable to Psionic attacks. Finally, they tend to attack in large mobs (average number of troops is 16).
They appear during raids on their temples and during their retaliations against X-COM's bases. Due to the cult's general hostile attitude towards X-COM it will be very likely for both sides to engage in raids since raiding their temples can be very profitous (and dangerous) to X-COM.
Cult members are moderately armed (starting Tech Level 2), but will improve over time. They are lightly armoured, but are more resistant to Psionic attacks than other humans. Cult members fight in groups of around 10.
Like cultists, gang members are also dangerous. Their slums are packed with shock troopers equipped with the biggest weapons around (starting Tech Level 4) and they'll regularly engage in raids against other organizations. Gang members attack in groups of 8-20 - Osiron groups are the largest, Psyke groups are the smallest.
These compose the security forces employed by the Government and all major legal corporations and organizations. Their armament and numbers depend on which organization employs them. In particular, the Government, Marsec, Solmine, Cyberweb, S.E.L.F. and the Mutant Alliance use better-equipped and larger groups of guards.
Security guards are not as weak as you might think, and their stats are only slightly lower than those of Megapol or Gang members. Starting Tech Level varies from 1 to 4 (although most organizations are at the lower end of the scale), and the average number of guards can range anywhere from 7 to 14.
Some organizations may employ guards with different coloured uniforms. This difference is purely cosmetic, and has no effect on stats or equipment.
Civilians will be found on every Mega-Primus mission that involves an alien investigation on a building. They won't take cover, they will run as if in panic without a direction.
Of particular note is that the aliens don't actively attack them. This is fortuitous for X-COM, however the various civilian deaths that do occur are frequently caused during a crossfire between X-COM and any hostile forces in the area. The best way to prevent civilian deaths is to move the battle away from the civilians.
Civilians do not otherwise count towards the mission score.
X-COM Technical Personnel
During base defense missions any X-COM Scientists and Engineers assigned to the base will be vulnerable to hostile agression. X-COM personnel can be directed to move to any location but they will be unable to use any weapons or armour. They are also slower than X-com Agents, which makes them quite vulnerable.
Survival of X-COM personnel is one of the highest priorities for X-COM Agents while repelling raids. Because technical staff can be assigned to armed personnel before the base raids begin, it is recommended that some armed agents accompany them and escort them to a place of safety in the base.