The suspected serial killer of four London men he met on gay dating websites is facing new charges of drugging and sexually assaulting eight others.

Prosecutors unveiled the extra charges Monday against Stephen Port, who already faces murder charges in connection with the discovery of four bodies near Port's home in Barking, east London, between June 2014 and September 2015. They say Port gave each victim in their 20s fatal doses of the psychoactive drug GHB.

The 41-year-old Port has pleaded not guilty and faces trial in October.

At Monday's court hearing, prosecutors accused Port of nonlethal attacks on eight other men involving six criminal counts of poisoning, seven of rape and four of sexual assault.

The police complaints watchdog is investigating why detectives did not initially link the killings.