These latches are operated by cables for the inside handles and by rods for the outside handles. Usually the latch itself is the cause of the problem when the section that controls the cables binds up.
Sometimes after someone removes the door panel they will forget to hook the cable ends back into the inside of the handle. The handle assembly is built into the door panel and pulls one cable to open the door and one cable lock and unlock. That would be the best case scenario. The worst case is having to replace the latch assembly located inside the edge of the door where it grabs the striker on the body.
You could start by removing the door panel (See Video Below) and checking if the cables are properly installed and if the handle is intact (viewing from the inner side of the door panel). Then pull the cable (while disconnected) when sitting in the front seat with the door closed. If the door doesn't open when you pull hard on the cable, the problem is most likely the latch. If it does open, check the handle itself for cracks or breaks. Just make sure the door is unlocked when checking this way.
I've done many of these on 2002 Altimas as well as Muranos, it is a fairly common problem. If you have any other issues with this I'll be happy to help you.