Police tonight made two more arrests in connection with the savage double murder of French students Laurent Bonomo and Gabriel Ferez.
Scotland Yard said a 35-year-old man and a 25-year-old woman were arrested at an address in Streatham, south London.
Earlier, police charged unemployed Nigel Edward Farmer, 33, of no fixed address, with the murders.
The badly-burned bodies of the two 23-year-old students were found after an explosion at a rented bedsit in New Cross on Sunday 29 June.
A police spokesman said: "The two people arrested - a 35-year-old man and a 25-year-old woman - were arrested at approximately 5.20pm today at an address in Streatham.
"Both were taken to a South London police station, where they remain in custody."
Farmer will appear at Greenwich magistrates' court tomorrow.
He is also charged with arson and attempting to pervert the course of justice, the Metropolitan Police said.
Detectives arrested Farmer after he walked into Lewisham police station in the early hours of Monday morning.
He was initially taken to hospital under guard for treatment to serious burns to his hands and arms.
Investigators found the victims had been bound, gagged and tortured before petrol or a similar inflammable liquid was splashed on and around their bodies.
Police said a strong smell of accelerant remained at the property hours after the blaze had been put out by firefighters.
Officers said forensic work at the ground-floor in Sterling Gardens property could continue for several more weeks.
Detectives have renewed their appeal for witnesses who may have seen anyone at the property on the day of the attacks.
Mr Bonomo was stabbed nearly 200 times, up to 80 of the wounds inflicted after he was dead, while Mr Ferez suffered nearly 50 knife wounds.
Six days earlier, Mr Bonomo disturbed an intruder stealing a laptop computer.
Experts found no evidence of forced entry after the murders, suggesting that keys might also have been stolen.
Two Sony handheld games consoles were also taken and credit cards are believed to be missing.