To the extent it constitutes legal evidence, it may be less believable precisely because this give police commissioners power that they may be exercising in corrupt and power-hungry ways.

You need to consider costs as well. The cost of a legal statment is much higher, in that the commissioner faces perjury charges if he utters a lie in court. But most importantly of all, is expected to back up his statement with solid evidence or a solid story of how he came to believe that X is a kingpin (both of which increase the chance of him being found out, if he is indeed lying).