A man wanted in connection with the 2005 murder of British police officer Sharon Beshenivsky has been arrested in Pakistan, the UK's West Yorkshire police said.
Ms Beshenivsky, 38, died after being shot when trying to stop a gang robbing a travel agent in Bradford, northern England 15 years ago. Her colleague Teresa Milburn was shot in the chest but survived.
Ms Beshenivsky had only been an officer for nine months when she was shot in the chest on what was her youngest daughter Lydia's fourth birthday.
Piran Ditta Khan, 71, was arrested as a result of coordination between police in Britain and Pakistan and appeared in court in Islamabad on Wednesday.
Detective Superintendent Mark Swift called Ditta Khan's arrest a "major development" in the long-running investigation.
"We are continuing to liaise with partners in Pakistan to process Khan's extradition with the intention of returning him to the UK to face court proceedings," he said.
In 2009, Mustaf Jama was jailed for life after being found guilty of Beshenivsky's murder. Five other defendants were convicted in 2006 for their parts in the robbery and killing.
Jama had fled to Somalia after the shooting and was extradited in 2007.