Rear speaker wiring

The rear speaker wires on my girlfriends malibu seem to have disappeared.

The previous owner of the car had put an aftermarket sound system in, and it appears as if the original wiring was ripped out. Nice, huh?

I have not heard of the original wiring being removed before (but usually I find that something like this would happen to me...), so I would like to know where the wiring is supposed to come from, and attempt to locate it (assuming it is still there). I would have to assume it got stuffed into wherever it came out of to make less of a mess of things.

So, where do the wires come out from to connect to the rear speakers? The sides of the trunk, down from the backboard, ect.

Where is the best place to run the wires if the originals no longer exist?

Thanks.