The Special Investigations Unit (SIU) is investigating a recent incident, leading to the arrested individual being put in hospital.
On Sunday just after 1 p.m., a London police officer found and arrested a 39-year-old man wanted by an unnamed outside agency, related to out-of-town warrants.
The agency was contacted, and the man was taken to police headquarters around 2 p.m.
The SIU said custody of the man was transferred to the outside agency around 2:40 p.m. but while he was in custody, his condition worsened.
He was taken to hospital but has since been discharged.
The SIU continues its investigation.