There was an interesting 15-minute programme on Radio 4 a couple of days ago about forensic acoustics (listen here for a few days more; thanks to Chris for sending me the link). Professor Peter French of York University was talking about some of the criminal cases he had been involved with.
In the late 1970s during a long hunt for the so-called Yorkshire Ripper, who murdered thirteen women and attacked several others, West Yorkshire police were led on a wild goose chase by tape recordings purportedly sent to them by the murderer. The person on the tape had a Sunderland accent and police put all their eggs into this basket and looked for a man from this locality. The tapes turned out to be hoaxes, but the linguist who had identified the voice as being from a particular region of Sunderland was spot on. On the aforementioned radio programme we heard both the original tape and the same words spoken by the same man twenty years or so later after he had been caught and imprisoned. The voices were still recognisably the same, despite the length of time that had passed and despite the fact that the owner of the voice was a heavy smoker and drinker, factors known to affect the voice.
Another murder featured in the programme -- the killer being Richard Garner, who murdered his father Frank. He made a number of phone calls to banks to withdraw money from his father's account but, despite the fact that he tried to disguise his Yorkshire accent, he made numerous slips which gave him away. These recordings featured in the radio programme.
Professor French said that the majority of the work of his department these days is to do with terrorism. A few years ago the main thrust of his work was drug crime. He also has a lot to do with the emergency services as he said that, since so many people carry mobile phones these days, and their first impulse is to phone the police, often their own attack and possibly even murder is recorded unwittingly as the line remains open.
The programme is available for a few more days here.