Law enforcement agencies will not release names or motives of individuals or groups involved in mass attacks to press.

Releasing the names and motivations of individuals or groups the attack the masses to the press provides those individuals and groups with an incentive to advance their platform. By not releasing information related to the perpetator(s), the attention can remain on the victims and away from the cause/attention grab of the culprit which could be an individual or potentially even a terrorist group.
The names and motivations can remain with the investigators, but not be public information for an extended period of time if ever.
There is a related precedent in the media with the names of minors not being released when they commit or are accused of committing a crime.