A 22-year-old man was arrested in connection with the fatal stabbing of a "bright and popular" teenager on a crowded bus as she travelled to school.
Christina Edkins, 16, was killed shortly after she boarded the double decker in rush hour this morning in an apparent random attack.
Police launched a manhunt for a fellow passenger who fled the scene and later arrested a man after a "short foot chase."
The stabbing happened a month after the teenager voiced concerns about a fellow passenger on another bus journey, she tweeted:
There is no suggestion that her concerns on February 8 are connected to today's attack.
However, West Midlands Police tweeted that they were "looking into" Miss Edkins' social media accounts.
Emergency services were called to Hagley Road, in Birmingham, at 7.37am this morning when the bus driver raised the alarm. Medics rushed to the scene but could not save her.
The teenager, who wasa pupil at Leasowes High School in Halesowen, West Midlands, is not believed to have known her assailant, who was supposedly already on the bus when she got on board.
West Midlands Police Detective Superintendent Richard Baker said detectives were looking into the theory that her murder was a random attack and added that officers were considering a number of possible motives.
"This is a tragic case and the victim's family are devastated," he said.
The arrested man was detained after an extensive search involving dogs and firearms officers.
He was arrested on suspicion of murder following a chase after he was seen acting suspiciously near a Morrison's supermarket.
Neil Shaw, the headteacher of Leasowes High School, led tributes to his pupil and said friends and family were "deeply saddened" by her death.
Flowers were left near the scene on Hagley Road this evening, some of the tributes read: