8 March 2013 Last updated at 09:57 ET

Christina Edkins bus stabbing: Single stab wound killed teenager

Christina was described as a "bright and popular student" by her head teacher

A 16-year-old girl who was attacked on rush-hour bus in Birmingham died from a single stab wound to the chest, post-mortem tests have revealed.

Christina Edkins was stabbed upstairs on the bus on Hagley Road while on her way to school in Halesowen on Thursday.

Officers are continuing to question a 22-year-old man from the Walsall area who was arrested near the scene of the stabbing a few hours later.

West Midlands Police are investigating whether it was a random attack.

They said they were not looking for anyone else in connection with the killing.

Earlier, the force said about 16 people were on the bus at the time of the attack but they had only spoken to half of them.

Pupils at Leasowes High School have mourned the death of Christina Edkins

They urged the other passengers to contact them urgently, even if they did not see the stabbing and had been sitting downstairs.

Officers said they believed Christina's attacker may have travelled on buses around the Birmingham area after the stabbing.

'Much loved'

Officers have released a CCTV image of a man wearing a jacket with a tiger design on the back and have urged anyone who saw him on Thursday between 0600 GMT and 1300 GMT to contact them.

West Midlands Police said extra officers were patrolling buses on Friday to reassure passengers.

Counsellors have been brought in to support pupils and staff at Leasowes High School, where Christina was a pupil.

Flowers, soft toys and balloons have been left outside the school.

Police released a CCTV image of a man in a jacket with a tiger design

The school said it thanked "everyone for many offers of support" and extended heartfelt sympathy to Christina's family.

A book of remembrance has been opened at nearby St Peter's Church, in Lapal, Halesowen, where people can go to light a candle.

Christina's head teacher Neil Shaw described her as a "bright and popular student" who was "much loved by staff and students".

'Distressed and distraught'

The Reverend Mike Rutter, the vicar of St Peter's, said: "It's a terrible tragedy and many in our community will be affected.

"Our thoughts and prayers are with Christina's family and friends at this difficult time."

Det Supt Richard Baker said the teenager's family were distressed and distraught.

At the scene

Frankie McCamley BBC WM reporter

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Outside Christina's school, queues of pupils have been turning up with flowers, balloons and teddy bears all morning. There are hundreds of flowers now outside the school gates.

There is none of the usual hustle and bustle you would expect during a school day. Instead, all the children are very visibly upset.

Flowers have also been left by the bus stop where the attack happened.

Christina's school friends want to do something in her memory. There has been talk of lots of things, including holding the school prom in her memory.

It is a very, very sombre atmosphere and very quiet. The community is taking this very hard.

Halesowen and Rowley Regis MP James Morris said he would be meeting officials of National Express later to discuss bus safety.

He added: "The whole community is in shock here in Halesowen about this tragedy."

Police said they would be checking Christina's profiles on social media websites as part of the investigation, but there was nothing to suggest she was being targeted.

She is understood to have boarded the bus minutes before the attack, which happened at about 07:40 GMT.

The driver raised the alarm and attempts were made to revive the teenager, but she died at the scene.

Police have urged any further witnesses to contact them.

The 22-year-old was arrested near the Morrisons supermarket at Five Ways at about 12:30 GMT.

Ch Insp Kerry Blakeman, head of operations for Safer Travel, an organisation run by West Midlands Police, British Transport Police and Centro, said Birmingham's buses were safe to travel on.

He said: "If you feel uncomfortable with anything, contact the driver.

"There is a reporting mechanism between the buses and the police and officers can be contacted immediately."