A teenager has been arrested on suspicion of robbery in connection with an attack on two schoolgirls which was viewed six million times on Facebook.
West Midlands Police said the 16-year-old was detained after visiting a police station.
She remained in custody on Tuesday evening.
The force said it also planned to arrest a second suspect over Saturday night’s attack, which was recorded in Sir Herbert Austin Way, Northfield.
Two other people – including a young man it said filmed the incident – have been spoken to by officers.
They film showed the victims being attacked being while their bags were grabbed and emptied as a laughing crowd looked on.
The pair were also forced to their knees to apologise for “giving dirty looks”.
The arrest came after members of the public who watched the Facebook footage provided details of those allegedly involved to police.
A West Midlands Police spokesman thanked the public for their help – but urged social media users to delete the video from their accounts.
The force said: “We would like to thank everyone who supported our enquiry and came forward with information.
“This was an upsetting incident for the two girls involved.
“Out of respect to them we would ask anyone who has shared the video to remove it from their profiles.
“The sharing of the video may also impact upon any future legal proceedings that may take place.
“Detectives have already spoken to two others of the group involved and plans are in place to arrest another girl involved.
“The response from members of the public, clearly disgusted by what they’ve seen online, has been overwhelming and we’ve had lots of people getting in touch to provide names of those responsible.
“This has led us to making an arrest this afternoon.
“I would like to reassure everyone this is being treated very seriously and that the enquiry is progressing quickly.”
The force earlier urged viewers outraged by the footage not to take the law into their own hands .
Threats were made against one girl accused of involvement in the attack on Twitter .
The incident was also condemned by the NSPCC .
A spokesman said: “The bullying in this video is sickening and it’s quite right that police are taking action against those involved.”
“Bullying is extremely distressing for children and young people and can leave them feeling anxious, lonely and scared.
“When videos like this are then shared on social media the victim’s suffering and humiliation is compounded.
“Facebook and other social media companies must take responsibility and remove this kind of material to avoid causing further distress.
“ChildLine is there to support any child or young person affected by bullying.”
ChildLine can be contacted on 0800 1111 or at.