I don't know what the guidelines are on that. Maybe they aren't allowed to release the mugshot before the trial and it can only be released afterwards or in this case after he pleaded guilty? I don't recall any murder suspect in this country ever having their mugshot released before the trial, so with regards to this case the only photos available were old ones. Nothing misleading about that IMO. After all, the severity of the crime speaks for itself, although his mugshot definitely adds to the horror of what happened.
Edit: Here you go mate:
Specifically in respect of images, the police, as the legal copyright owner, are responsible for releasing an offender’s custody photograph. The image may be released upon a guilty verdict unless there is a court order or legitimate policing purpose preventing their identification. Images may be released as soon as possible after the verdict to allow the media to publish them contemporaneously, i.e., in their next available edition or broadcast.The image can be released again upon sentence if necessary.