One person was killed and seven others were injured when a knifeman went on a 90-minute rampage in the city centre.
West Midlands Police has released CCTV footage of a man they want to speak to.
Chief Superintendent Steve Graham said: “We are appealing for anyone who recognises the man in the footage to contact us urgently.
“If you see him, please do not approach him, but dial 999 immediately.”
In the CCTV footage, a man is shown wearing a baseball cap and zip-up hoodie.
He is also wearing dark-coloured trousers and shoes and can be seen standing and walking on a street corner.
The force declared a major incident after being called to reports of a stabbing just after midnight on Sunday before being alerted to further attacks.
An urgent manhunt is underway to catch a male suspect.
Mr Graham said the incidents appeared to be “random”, with “no suggestion” they were linked to terrorism.
He said: “A man has tragically died.
“Another man and a woman have suffered serious injuries and five others have also been injured, although their injuries are not thought to be life-threatening.”
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