The law states that an individual is innocent until proven guilty. Covering their faces insures (somewhat) that they won't be tried in the court of public opinion prior to having legal representation. Each situation is different.
The UK conceals identities of minors who are accused of crimes - sometimes right up to the point of the media having to take them to court after obtaining a conviction to get the ban on identifying the suspects overturned.
"Baby P" or Peter Connoley was a murder victim and both he and his murderer enjoyed anonymity until she was convinced and the ban was lifted.
