Mikias Tekeste, 30, died in hospital shortly after 11pm on July 15, after being arrested in Croydon town centre at 2.15pm.
Police watchdog the Independent Office for Police Conduct (IOPC) confirmed on Friday it has launched a criminal investigation into two officers who were travelling in a police van with Mr Tekeste, when he swallowed items hidden on his person.
The IOPC said the two constables “may have failed to appropriately supervise Mr Tekeste”.
The officers are being criminally investigated for potential gross negligence manslaughter, and investigators are also examining whether their behaviour amounted to gross misconduct on a professional level.
Mr Tekeste was arrested by Met officers in Croydon town centre on the afternoon of July 15, on recall to prison, and on suspicion of possession with intent to supply Class A drugs.
He was transported to the Croydon Custody Centre in a police vehicle.
In CCTV footage from inside the vehicle, that has since been reviewed by the IOPC, Mr Tekeste can be seen to remove items from his clothing before swallowing them.
Later that evening, staff noticed he appeared unwell in his cell at the custody centre. First aid was given by a medical professional and an ambulance was called.
Paramedics arrived minutes later and Mr Tekeste was taken to hospital, where he died the same night.
The criminal investigation against the two Met Police officers involved in the incident was announced by the IOPC on Friday.
“IOPC investigators have viewed CCTV from inside the police van that transported Mr Tekeste to custody following his arrest and have determined that two officers who were in the vehicle may have failed to appropriately supervise Mr Tekeste during this time,” said a spokesperson.
“As a result, we have advised two police constables that they are being criminally investigated for the potential offence of gross negligence manslaughter.
“The officers are also being investigated for potential breaches of the police standards of professional behaviour at the level of gross misconduct.
“This does not mean that criminal charges or disciplinary proceedings will necessarily follow.”
IOPC regional director Mel Palmer said: “Our thoughts and sympathies are with the family and friends of Mikias Tekeste. Our investigators have met with his family to inform them of this update.
“We are continuing to piece together the circumstances leading up to Mr Tekeste’s death and we are reviewing the actions of MPS staff beginning from his arrest in Croydon, to his transport to and subsequent detention in the custody suite.
“We have found no evidence of any inappropriate use of force during this period.
“At the end of our investigation we will decide whether to refer a file of evidence to the Crown Prosecution Service for a charging decision and also determine whether any MPS staff should face disciplinary proceedings.”
The IOPC says investigators have reviewed CCTV footage from the custody suite, and the police van Mr Tekeste was transported in.
They have also received ccounts from police staff involved, are are reviewing custody records from the day of the incident, along with relevant police policies and procedures.
The watchdog is awaiting results of a post-mortem, including a toxicology report that would reveal any substances that may have been in Mr Tekeste’s system when he died.
A date for the opening of his inquest is yet to be set.
Scotland Yard said the two officers under investigation will be on restricted duties while the probe is carried out.
A Met Police spokesperson said: “Any death in custody or following police contact is a serious matter and a cause of community concern. They rightly expect the circumstances to be fully investigated.
“We are providing every assistance to the IOPC investigation and our thoughts remain with Mr Tekeste’s family.
“The launching of an investigation is not in itself a finding of wrongdoing, however the officers will remain on restricted duties while the investigation is carried out.”