A 15-year-old boy has been arrested at a school over the murders of two policewomen killed in a gun and grenade attack.
The teenager was held 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.
A spokeswoman for Greater Manchester Police said: "Officers attended a school in the Hattersley area and they arrested a 15-year-old boy on suspicion of assisting an offender.
"He has been bailed until Thursday, September 27, pending further inquiries."
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."
Earlier on Friday, a massive security operation was mounted for the first court appearance of the man accused of the four murders and also four attempted murders.
The hearing for one-eyed Dale Cregan before a district judge lasted just two minutes as he was remanded in custody and taken back to Manchester's Strangeways prison.