You enter Liberty Mall through the back door in Kappel's boutique.
The Mall
Enter the boutique, and head around the barricades to reach the escalator. Climb it, and head around the escalator spacing to reach the exit of the store.
You can see a map of the mall just ahead; it doesn't show the direct path (which is blocked by various barricades) but gives a general idea of where you should go. The first step is taking the trip down the escalator, and heading to the next escalators. On the second floor are tunnels reserved for employees.
There are two possible routes, which vary based on the director. The direct path is the emergency exit into the mall proper, and the other requires you to shoot the windows in the Just for Kids store.
The Alarm
To disable the alarm, climb up any visibly staircase and head to the security office. As you approach, there will be one final hoard that charges toward you.
Head down the side corridor from the security office. From the corridor, return to the mall; the safe house can be reached on the uppermost floor by taking the right-hand path.
Respawn point
The only respawn point is within the security office, where you disable the alarm.