Summary: Using power fluctuations in the national grid police claim to be able to date a recording precisely. The fluctuations affect any mains connected equipment, and allegedly even battery powered devices.
The police seem to love this kind of highly dubious forensic evidence. Let’s look at their record.
Fingerprints – not unique and never a perfect match like on TV, in fact matching is very much an art. Unreliable.
DNA – started out as a 1 in 1,000,000,000 chance of a sample matching two people, now it turns out that even with a good sample it’s more like 1 in 1,000,000 (i.e. 60 other people in the UK match).
DNA amplification – taking a small sample of DNA and build it up. The Omagh bombing trial collapsed after it was revealed to be bunk.
Firearms residue – a single spec was enough to convict Barry George until it was revealed that it was worthless as evidence. An innocent man spends years in jail.
CCTV – video evidence is powerful and solves crimes, except that most of the time it doesn’t.
Lie detectors – need I even go into them?