On: London Met Police lab uses "electrical network frequency analysis" (ENF)

[daten]

Here's a white-paper with more detail about the technology.

http://www.diamondcut.com/Downloads/AppNote4DiamondCut.pdf

The author describes a case-work example where he compares an analyzed audio file to ENF data from the power company (?) about the building and can prove it wasn't recorded on the claimed date and there were multiple deletions.