Find the killer. Blend in with your surroundings and try not to make anyone uncomfortable around you. If provoked, the killer will silently infect a citizen with a virus; which, when provoked, will be prone to kill people who make them uncomfortable. Try to finish with as few casualties as possible.
The virus causes its victims to go mad, whilst retaining their personalities. It does cause them to become very dangerous though, and can even give the enemy an advantage to distract you from his actions.

What is Ether Proxy’s Progress?

Citizens monitor one another. Some citizens are naturally more nosy than others. Nosy citizens make people all the more wary around them. Citizens keeping to themselves will be less noticeable to others. Citizens looking around frequently in crowds are the converse. If a citizen feels uncomfortable, they will change seats and leave. If the enemy feels uncomfortable, they will infect somebody. If an infected citizen feels uncomfortable, they will target the source of their uneasiness. The player can make calls to send a menacing message, or fake a family member or loved one. This will increase or decrease their proclivity to appear suspicious. The player can utilize a base distraction, such as a newspaper, to reduce their outgoing suspiciousness.
The rest of the airport has yet to be opened up. You can not talk to citizens. Eventually you will be given guards who will help keep an eye open for you. Bathrooms have not been installed. Nor have planes. Nor has the shuttle, or your ability to ride on top of it unseen. No complex fight sequences have been added. No blood. No weapons citizens can use. No luggage to carry things. No characters in uniforms whom you can imitate to reduce suspiciousness. And most of all, the way in which citizens deem each other suspicious will undergo many improvements in the future.

I appreciate your interest! Please stick around for Ether Proxy to continue its evolution!