Assistant Chief Constable Rob Potts of Counter Terrorism Policing North West said the families of Mr Cravitz and Mr Daulby, as well as victims who survived serious injuries, had been informed of the latest arrest.
He added: “Our investigation is continuing, and I would once again appeal for anyone with information that they think could assist our enquiries to please come forward.
“We are also still seeking to identify and speak to anyone who was present at the time of the incident or the immediate aftermath so that we can ensure they have access to all the welfare support options that are available to witnesses.”
Last month Rabbi Daniel Walker, who alongside his congregants held the doors of the synagogue shut, said the empty seats where Mr Daulby and Mr Cravitz used to sit were one of the “first things I see” whenever he entered the building.
“They were both very, very special men,” he told the BBC.
“Adrian was a very quiet man – a man of great dignity, always with a smile, always kind, very much loved by his family and his neighbours.
“Melvin was also a wonderful man – a family man.”