Greater Manchester Police Assistant Chief Constable Garry Shewan has revealed details of an arrest made over an offensive Facebook page created after the deaths of PC Fiona Bone and PC Nicola Hughes.
Speaking at news conference, he said an investigation by Greater Manchester Police and Merseyside Police led to the arrest of a 22-year-old man from Merseyside last night.
He remains in custody and is being questioned.
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A humid night for some with thundery downpours in places.
The 20-year-old was found fatally wounded on Roth Walk, near Finsbury Park, north London at around 3am on Saturday, Scotland Yard said.
Daniel Cowell has been jailed for five years and four months after ramming a police patrol car with a stolen transit van.