General assumptions: You must use all two disguises available in the fourth game mission.
It is very hard to obtain Chicago SWAT officer disguise. You encounter SWAT member only in Train station stage, during your stay in the residential building. Try to surprise the opponent who walks at the very end of the SWAT group heading to the elevator or start the fight and during it quickly obtain the disguise.
Chicago policeman disguise is in turn very easy to obtain because you can get rid of any officer encounter in the Run For Your Life mission.
General assumptions: You must find three evidences.
First evidence can be obtained in The Library stage. It is located on the ground floor, in the second part of the library, near the place where a new group of cops appears.
The second evidence can be obtained in the Shangri-La stage. It is located near the exit from a room with two junkies and two cops.
The third evidence can be obtained in the Train station stage. It's located in residential building lobby and it is vest to get it in policeman disguise.
General assumptions: You can't be spotted. In order to complete this challenge in 100% you have to do this in each of five stages of the fourth mission. The most problematic will be probably The Library and Train station stages, because you can be easily exposed there. So I recommend using policeman disguise. It is also worth noting that the escape from a helicopter in Pigeon coop stage is not treated as being spotted.
General assumptions: You can't use disguises. In order to complete this challenge in 100% you have to do this in each of five stages of the fourth mission. Same as above, it is hard to stay in a default Hitman suit in The Library and Train station stages. So as a result, you can complete these stages on lower difficulty levels or spend much time to learn policemen paths so you can skillfully sneak past them.
Picking on the New Guy
General assumptions: You must take a hostage in the library and get with him to the exit.
This challenge must be completed in The Library stage. Make sure that you have firearms, select it in the inventory and then take any cop from behind, taking him as hostage (human shield). Now you have get with this person to the library exit and it is best to move along the wall, so no one can surprise Hitman from behind.
Death From Above
General assumptions: You must use a chandelier to kill enemy.
A chance to complete that challenge appears in The Library stage. Depending on your preferences you can use a lever to release the chandelier or shoot its chain. The challenge is completed when the chandelier kills at least one cop.
Fields of Joy
General assumptions: You must cross the marijuana field while not being spotted.
The marijuana field is located in the residential building occupied by junkies. You can find it in the Shangri-La stage. It is very important to stay crouching and carefully observe actions of cops patrolling the area, keeping a safe distance from them.
General assumptions: You must kill three persons with bong.
This challenge can be completed in Shangri-La stage. Each time you have to start with finding a bong. First of them is located in a room with two junkies and two cops.
Second bong is located in a small kitchen adjacent to the marijuana field.
The third bong is located in a room with a tape player (left from the elevator).
After you obtained a bong, use it to kill any junkie or cop. Important information is that bong is breakable so you must find another one after successful kill.
Business is Booming
General assumptions: You must lure policemen to the safe in a residential building.
This challenge can be completed in the residential building occupied by junkies - Shangri-La stage. Explore two rooms located on the right from the elevator, finding a safe in one of them. Wait until the policeman leaves the room, look around for the notebook and then open the safe.
Switch on the radio, hide and watch events. The challenge is completed when all nearby cops enters the room (you do not have to do anything else).
General assumptions: Lure the policemen with music in the residential building.
A place to complete this challenge is a residential building occupied by junkies in Shangri-La stage. Explore the room located left from the elevator and interact with tape player in order to switch on the music.
Hide and watch events. The challenge is completed when all nearby cops enters the room (you do not have to do anything else).
The Tables Have Turned
General assumptions: This challenge is automatically unlocked after completing the Run For Your Life mission.
Silence Please Part 1
General assumptions: You must eliminate an opponent in the library and hide the body.
This challenge can be completed in the second stage of this mission - The Library. Surprise from behind any cop here and stun him (not kill!). After that, hide his body in a closet in a crate.
Silence Please Part 2
General assumptions: You must eliminate seven opponents in the library and hide their body. This challenge is an extensive version of previous one.