It would be unlikely for LE to announce further arrests, unless it advances their objectives.
The previous arrest, was on the back of a CCTV release from LE. LE announced the arrest in that instance as they would have been aware of the public mood concerning safety, following LB's tragic death, as well as the possible risk to incorrectly identified persons.
In some instances, authorisation may be given to hold someone 'incommunicado'. This is when no one is informed of the arrest for a period of time, when to do so may obstruct the investigation, e.g. evidence may be hidden, destroyed or other possible suspects may move elsewhere.