LONDON (AP) — Police investigating the mystery death of a British spy say they are hunting for two people seen entering his apartment block.

Gareth Williams was discovered dead at his home on Aug. 23. Officers said he had been dead for some time, and his naked remains were found inside a locked sports bag. No cause of death has been established.

The 30-year-old worked for GCHQ, Britain's eavesdropping service, and had been on assignment with the MI6 spy agency.

Detective Chief Inspector Jacqueline Sebire said on Monday that police are searching for a man and a woman seen entering the apartment block one night in June or July.

Police said there was no sign of forced entry, and no property was stolen.