A 22-year-old man from Merseyside has been arrested in connection with an offensive Facebook page set up, following the deaths of police officers Nicola Hughes and Fiona Bone, Greater Manchester Police said.
The "tribute" went online within hours of Pcs Nicola Hughes, 23, and Fiona Bone, 32, dying in a gun and grenade attack in Hattersley, Tameside, on Tuesday morning.
Some people had chosen to use social media in a "very malicious and offensive way", Greater Manchester Police (GMP) Assistant Chief Constable Garry Shewan said.
Greater Manchester Police announced the arrest as officers continued to question Cregan, 29, on suspicion of murder.
He was detained after walking into a nearby police station after the attack.
As tens of thousands of tributes poured in from across the nation for the fallen officers, more than one Facebook page was set up in praise of the suspect held by police.
From looking at the numerous websites containing derogatory and offensive comments, Mr Shewan said he saw "ordinary members of public alarmed and distressed at some of the ridiculous comments that have been put on there".
One was titled Dale Cregan OBE, with internet "trolls" posting messages claiming the alleged killer was a "hero".
32-year-old Fiona Bone and 23-year-old Nicola Hughes were killed after they responded to reports of a burglary
A warrant of further detention was obtained last night for Cregan and is due to expire at 9am tomorrow.
A 28-year-old man who was arrested yesterday in the Hattersley area on suspicion of conspiracy to commit murder also remains in police custody.
Today's Facebook arrest comes after Greater Manchester Police thanked the public and said officers took heart from the huge outpouring of goodwill and public support.
The force has received 33,500 messages on its online book of condolence, more than 21,000 have been posted on the force's Facebook page and more than 1.3 million people have viewed the tribute to the officers on Facebook.
The arrests come as the country's top prosecutor, Keir Starmer QC, said "the time has come for an informed debate about the boundaries of free speech in an age of social media".