A Metropolitan Police officer is being investigated for gross misconduct over the death of Rashan Charles in London, the police watchdog has said.
Mr Charles, 20, died after being apprehended by police officers in Dalston, east London, on 22 July.
He became ill after trying to swallow an object and was later pronounced dead in hospital.
The Met Police said it was vital to establish the truth of how Mr Charles died as quickly as possible.
A post-mortem examination found a package containing "a mixture of paracetamol and caffeine" in Mr Charles' throat.
Mr Charles' death led to angry clashes in Hackney with protesters hurling fireworks and bottles at riot police, blocking parts of Kingsland Road and setting mattresses alight.
On Wednesday the Independent Police Complaints Commission (IPCC) said it had formally notified the police officer that he was being investigated for gross misconduct.
IPCC commissioner Cindy Butts said: "The officer may have breached the police standards of professional behaviour regarding the detention and restraint of Rashan as well as how he dealt with Rashan's medical emergency.
"Our investigators have analysed the CCTV and body-worn video evidence we gathered and considered the officer's detailed statement as well as statements from other witnesses to the incident.
"We have also considered the relevant policies and procedures."
She added that while the IPCC investigation was moving into a new phase it did not "necessarily mean misconduct proceedings will follow".
In a statement the Metropolitan Police Service (MPS) said: "It is absolutely vital that the facts of what took place are thoroughly established as quickly as possible through an independent examination of all the available evidence.
"The thoughts of the MPS are with the family of Mr Charles at this incredibly difficult time for them.
"All police officers are fully aware that they will be asked to account for their actions. No officer is above the law and they would not wish to be."
The Met said the officer and other colleagues were fully co-operating with the IPCC investigation.
It added it was now reviewing what restrictions, if any, should be placed on the officer.