On e of the best and least intrusive methods for determining if there is rot and mold under the wallboard without doing a destructive examination is use a non contact IR thermometer and shoot a known (dry) wall and then shoot the front wall where the water is or where you think it's coming from.
If the IR says it's a couple degrees warmer than the known dry wall. You not only have a leak, you have rot,or soaked insulation or mold growing, probably all 3. Mold creates heat, rot creates heat, soaked insulation molds and creates hear. That space is dark and waem, great for growing mold.