The man arrested on suspicion of harassing a Brighton woman on Facebook is a serving police officer.
Lee Rimell, 32, from Birmingham, was arrested eight days ago (Tuesday 21 August) after Nicola Brookes, 45, won a High Court case forcing Facebook to reveal his identity.
She brought the case after being abused online after she posted a message of support for Frankie Cocozza, from Woodingdean, who was a contestant on the ITV show The X Factor.
Miss Brookes also believed that her Facebook account and e-mails had been hacked.
Her case was the first in Britain to lead to Facebook being ordered to disclose details about the identity of people known as cyberbullies or internet trolls.
Sussex Police was criticised for its handling of the case by the London firm of solicitors Bains Cohen.
The firm, who are representing Miss Brookes, said: “The police refused to help her despite her continued pleas for assistance.”
Rupinder Bains is Miss Brookes’s lawyer. She said: “It should have been the police’s job to get these details from Facebook but they have completely failed in their responsibility to do that.”
Rimell’s force said: “West Midlands Police is assisting Sussex Police in connection with an ongoing inquiry regarding a serving West Midlands police officer.
“The allegations do not relate to use of police systems.
“The officer has not been suspended and he is not a frontline officer.”
Sussex Police said that it had asked Facebook to remove any abusive posts about Miss Brookes.
It insisted that it took seriously allegations of bullying, harassment or malicious communication.