Police said on Sunday they are treating the murder of an Asian man near a mosque as a terrorist attack, and have arrested a man already being held over an alleged terror bombing campaign against Muslims.
Mohammed Saleem, 82, was stabbed to death in April as he walked the few hundred yards from a Birmingham mosque to his home with the aid of a stick.
Counter-terrorism detectives arrested a 25-year-old man on Saturday in connection with the murder, which they described as a "further act of terrorism".
He is one of two Ukrainian men who were arrested on Thursday over a series of three bomb attacks in a month on mosques in the West Midlands.
Saleem was stabbed three times in the back at 10.10pm on 29 April in the Small Heath area of Birmingham. Images taken from CCTV in the aftermath of the attack showed a white male wearing a cap running away and detectives said a racial motive was a line of inquiry.
Saleem's funeral, delayed because of the police investigation, was attended by more than 5,000 people.
On Saturday police said one of the two men arrested had also been arrested on suspicion of Saleem's murder.
Officers who were put on 12-hour shifts last week amid fears the bombers could strike again, a move the force itself described as extraordinary, have returned to working normal eight-hour shifts.
The investigation is being led by Assistant Chief Constable Marcus Beale, who said: "The murder of Mohammed Saleem now forms part of the wider West Midlands counter-terrorism unit investigation."
Detectives continue to examine if the murder of Saleem and the subsequent attacks against the mosques are linked.
They are also investigating whether those arrested had links to any groups, such as far-right violent extremists, in the UK or abroad. The men are believed to have only been in Britain for months, based at a Small Heath software company on a work placement. Its premises were searched by police who are understood to be investigating if there are any more devices or bomb-making material.
The Labour MP for Birmingham Ladywood, Shabana Mahmood, said: "I welcome the news that an arrest has been made in connection with the murder of Mr Saleem, a much-loved member of our community.
"Although nothing can bring him back, the fact that a significant step has been taken towards getting justice for Mr Saleem will be a comfort to his family and the community in Small Heath.
"It is shocking that Mr Saleem's brutal murder may have occurred as an act of terrorism and it is vital that the community continues to support the police as they progress their investigations."
Warrants to hold the two men for a further seven days under counter-terrorism laws were granted on Saturday by City of Westminster magistrates.
Shortly after Saleem's death, one of his daughters, Shazia Khan, said the attack was "a premeditated, brutal attack, pre-planned, intended to kill".
She added: "I cannot see him having any enemies being so full of hate to do this to him. He was an old man. He had no other agenda in his life. We just cannot understand it.
"We have to walk past where he was killed and we can visualise it we have to live with that for the rest of our lives."