The dog referred to in this case was trained to alert to human cadaverine only.
Yes, but actual evidence is needed to support the dogs alert, same as actual evidence is needed to support a sighting. Otherwise you have people facing charges and a lot of jail time because they were convicted due to very flimsy unsubstantiated testimony.
Take eye witness testimony for example, it is notoriously unreliable. You cannot prosecute someone because a dog alerts, this is not evidence, you need actual evidence, eg DNA, to back it up. Without that you have nothing - a dog that barked or sat down, whatever.