A 15-year-old boy was arrested at a school over the murders of two policewomen killed in a gun and grenade attack.
The teenager was held yesterday on suspicion of assisting an offender and questioned by police investigating the deaths of Pc Nicola Hughes, 23, and Pc Fiona Bone, 32, and father and son David and Mark Short.
He was later released on bail pending further inquiries.
The officers died on Tuesday after they were called to a report of a burglary in Hattersley, Greater Manchester .
Mr Short and his son were murdered in separate incidents earlier this year in Clayton and Droylsden.
Greater Manchester Police said officers attended a school in the Hattersley area yesterday afternoon.
Assistant Chief Constable Garry Shewan said: "This remains a complex and sensitive operation and we continue to ask the public to search their conscience and urge anyone who has any other information to contact us."
There was a massive security operation for the first court appearance of Dale Cregan, who is accused of the four murders and also four attempted murders.
The hearing for one-eyed Cregan before a district judge lasted just two minutes as he was remanded in custody and taken to Manchester 's Strangeways prison.
Cregan, 29, sat down as he was brought into the dock at Manchester Magistrates' Court but got to his feet after he was asked to stand by District Judge Jonathan Taaffe.
He wore a false black onyx eye in his left eye socket and spoke only to confirm his name and date of birth to the courtroom, which was packed with reporters.
Judge Taaffe then read out the eight charges the defendant faces.
The proceedings were held amid a ring of steel as officers in high-visibility yellow jackets stood guard on street corners around the city centre building.
Inside the court complex, armed officers wearing dark glasses, black uniforms and carrying Heckler and Koch machine guns stood guard.
There were more armed officers outside court number 16, the courtroom where Cregan appeared after he arrived in a convoy of police vehicles and into an underground car park.
Cregan was brought into the secure dock flanked by four police officers.
Two more officers dressed in military-style fatigues and armed with machine guns stood outside the dock.
Cregan, who has grown a thick beard, scanned the courtroom and the public gallery.
Mark Short, 23, died from a gunshot wound to his neck after a gunman entered a pub and opened fire, around 11.50pm at the the Cotton Tree Inn, on Market Street, in Droylsden, Tameside, on May 25.
Cregan is also accused of the attempted murders of Michael Belcher, Ryan Pridding and John Short, who were in the pub at the time.
Eleven weeks later, on August 10, the victim's father, David Short, 46, died in a grenade and gun attack on his home on Folkestone Road East, in Clayton, Manchester , at around 10.30am.
Less than 10 minutes later on the same day there was another grenade explosion less than half a mile away on Luke Road, Droylsden.
Cregan faces a further allegation of the attempted murder of Sharon Hark arising from the incidents on that day.
He will next appear at Manchester Crown Court on Monday.
David Cameron later visited the headquarters of Greater Manchester Police where he had private talks with the families of the two policewomen together.
The Prime Minister said: "I wanted to come here to Manchester myself to pay my own personal respects to the two officers, the women police officers, who fell in the line of duty.
"I think the whole country is profoundly shocked by what has happened and it is right we praise the work that they did and remember all they have done."
Mr Cameron was briefed about the ongoing investigation by Sir Peter Fahy, GMP's Chief Constable, and also recorded an internal message on camera to officers of the force.
A 28-year-old man arrested on suspicion of conspiracy to commit murder was released without charge, police also revealed.
Following the deaths of the officers, the Greater Manchester force received more than 30,000 messages on its online book of condolence, more than 20,000 messages on the force's Facebook page and more than 1.3 million people have viewed the tribute to the officers on Facebook.
Police from across the country have also offered to provide cover so officers can attend the funerals of Pcs Bone and Hughes.