Police are trying to piece together the movements of the chief suspect in the stabbing of 16-year-old schoolgirl Christina Edkins.
A CCTV image of the suspect wearing a black jacket with a distinctive tiger motif on it was released by police in Birmingham in an attempt to try to track his movements before and after the attack.
Christina was killed on a busy double-decker bus as she travelled to school during rush hour in what police branded a "senseless and random" attack.
Speaking at a news conference, Detective Superintendent Richard Baker said that they believed that the man "continued using buses in the hours after the tragic event".
Det Supt Baker also appealed for witnesses to the attack saying there were 16 people travelling on the number 9 bus when the attack happened but that only half of them had spoken to police.
He said: "We know there are a number of passengers who were on the bus yesterday morning 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. They may not even have known what happened but may have vital evidence and it is crucial they contact us as soon as possible on 101."
Christina died of a single stab wound to the chest, a post-mortem examination found.
A woman claiming to have witnessed the attack on the bus said she waited for the girl's attacker to get off the vehicle before performing CPR (cardiopulmonary resuscitation) on the teenager.
Writing on Facebook, Stephanie Bent said: "I was on that bus i knew what he had done and he was stood next to me when he was getting off, all i could think of was i hope he gets off this stop so i can go upstairs and help the girl.
"Thankfully he got off and i was able to go upstairs and help the girl as best i could i gave CPR until medics arrived and am deeply traumatised i could not save her, i certainly wasn't going to confront a knifeman knowing he had just stabbed someone i thought me may stab me too all i cared about was getting up to the girl to help."
Officers are continuing to question a 22-year-old man who was arrested after a manhunt was launched following the 7.30am stabbing and were granted an extra 12 hours to detain him.
Police today provided extra patrols on public transport after the attack prompted concerns among residents about knife crime and many voiced fears over travelling on the city's transport system on social network sites.
Christina, who was described as a "bright and popular" pupil at Leasowes High School in Halesowen, was killed shortly after she boarded the double-decker.
The stabbing happened nearly a month after the teenager had voiced concerns on Twitter about the behaviour of a passenger on another bus trip.
On February 8 she wrote: "This man is worrying me on the bus keeps getting up and walking up and down stairs, and sitting in different place."
However, police said there was no evidence to suggest Christina knew her attacker but that they were aware of her "social media presence".
Police officers stood guard at the Edkins' semi-detached house near Birmingham city centre for much of the day on Thursday while family liaison officers sought to comfort relatives.
Neil Shaw, the headteacher of Leasowes High School, led tributes to his pupil and said friends and family were "deeply saddened" by her death.