Detectives investigating the murder of a city schoolgirl have told how her killer silently stabbed her once in the chest - before casually stepping off the Number 9 bus.
And officers revealed a tiger jacket wearing suspect may have travelled on other buses around the city for more than FIVE HOURS after the fatal attack.
Police said no words were spoken between tragic Christina Edkins, 16, and the man who fatally stabbed her on Thursday morning in the "senseless" and "completely random" murder.
They also revealed that a schoolboy was the sole eyewitness to the murder. He was sat at the back of the top deck of the bus as it pulled into Hagley Road stop at 7.37am.
Detective Superintendent Richard Baker, who is heading up the major crime team at Force CID, confirmed that officers had recovered bus CCTV footage of the murder.
He said: "Three people who were sat on the top deck of the bus. They were Christina, the alleged killer who was sat behind her and was already on the bus when she boarded and a schoolboy who was sat on the back row.
"There was no conversation at all between Christina and the man who attacked her.
"The man stood up as the bus approached the stop and stabbed her once in the chest as he walked past her. This was not a frenzied attack.
"The bus was in the process of stopping when the attack took place and only lasted one or two seconds.
"The attacker casually walked off the bus after the attack."
Christina had boarded the Number 9 after walking from her home in St Mary's Crescent, Ladywood, where she had lived with mum and dad, Jason and Kathleen.
There were 16 people on the bus and officers are still looking to trace at least six passengers who may not have even known that the attack took place.
Det Supt Baker added: "We have spoken to the schoolboy who witnessed the incident and he is being given counselling.
"It appears that he may have not realised that Christina had been stabbed. Christina called out for help and the eyewitness went to her aid to see what had happened and he alerted the driver.
"We know there are a number of passengers who were on the bus when Christina was attacked while she was sitting upstairs.
"Some of these passengers were sitting downstairs on the bus and they haven't yet spoken to police.
"It is very possible that the other passengers were not aware of what happened upstairs and we would urge them to come forward and speak to us urgently.
"We have been told that those that heard the scream thought it was teenagers messing around.
"They may not even have known what happened but may have vital evidence and it is crucial they contact us as soon as possible."
Yesterday police released footage of a suspect calmly leaving the bus after the attack in a bid to trace his movements.
The man, wearing a distinctive tiger-motif jacket, is believed to have been travelling on buses in and around the Birmingham area between 6am and 1pm.
The suspect is described as black, aged in his early 20s, and was carrying a white bag.
Det Supt Baker said: "We believe the suspect was travelling on buses throughout Birmingham and the West Midlands throughout the morning.
"We would urge anybody who saw this man at any point on Thursday to contact us. Regardless of how unimportant you may feel this information is, we need to hear from you.
"Thursday's events were truly tragic and it's extremely important everyone comes forward and speaks to us.
"We will also be able to signpost them to professional agencies who can help them come to terms with being witness to such a tragedy."
A 22-year-old man was last night sectioned under the Mental health Act. He was arrested on Thursday afternoon and was being questioned by police on suspicion of murder.
Police also confirmed that they were not looking for anyone else in connection with this incident.