Why a leaking waste line ?

wastle line leak

While in the crawlspace of this home, I found a puddle of moisture below the waste line from the floor 2 main bathroom.

Going back thru the bathroom, there were no visible leaks.  If the toilet or tub drains were leaking, there should also have been evidence at the ceiling above the Dining room as these fixtures were about 5 feet away from the drain line.

Using thermal imagery, I located the waste line in the Dining room wall (by running hot water in the bathtub of the main bathroom).

The waste line was located where expected.  There was an anomaly to the infrared detection;

About 1/3 of the distance down the wall, the temperature detected increased.  At this location is a nail driven in the wall for a picture. The nail appears to have been driven into the waste line. Sewage water is leaking into the wall cavity and then into the crawlspace.  The carpeting in this room had been removed for unknown reasons (as it is a bank owned property)