Because I find it difficult
Look up a walkthrough.
I think it was the last one that I fugured out…
Out the room immediatly, enter the first room on the right as you ran forwad from your room, jump to the other rooftop, wait there until the map says the swat team left the floor you were in. As swat leaves, go back to the building you were in and take the stairs in the north to go down one floor. Use sedative syringe on a cop that is guarding a crime scene on that floor and dress like him. Get the sedative syringe on the crime scene. Get out of the building. Look for the firefighter on the northwest, sedate him and dress like him. Find the keys to the ambulance (don’t remember where. Maybe someone else as them). Leave.
Don’t forget about Albert Fournier!
That sums it up pretty well.
Some additional notes:
You don’t need to wait until the SWAT leaves. Just wait until the SWAT is looking at your door. Then jump back into the apartment behind them. You should be able to sneak to a fuse box at the end of the corridor without anyone noticing. Switch if off and you can walk down the stairs to the floor with the lone cop without anyone noticing.
To get your target you need to lure away the SWAT officers around him. For this you need to trigger a car alarm via a gun shoot. You can find a silenced pistol on the crime scene. Make sure none of the police officers sees you when you fire at the car. Once the alarm goes off, you have a short window to kill your target and leave without anyone noticing. Just put a bullet in his head and run to the ambulance. Don’t worry about the civilians behind the target. They neither count as witnesses nor do they alarm any cops.