A £20,000 reward is being offered to help catch a man who murdered a woman in east London and carried out three further sex attacks.
Michelle Samaraweera, 35, was raped before her body was found in Queens Road park in Walthamstow in May 2009.
DNA evidence has confirmed her killer had carried out three other rapes.
Last month police released CCTV images of a man they want to trace who was seen going into a shop soon after Miss Samaraweera, the night she died.
The man was seen entering Somerfield supermarket in Markshouse Road at about 0100 BST while Miss Samaraweera was still inside the shop.
Police said the man was of Asian appearance, or with dark skin and dark hair, and aged between 30 and 45.
Det Ch Insp Stewart Hill, said: "We are now offering this large reward in a bid to trace the man responsible for Michelle's callous murder and the linked assaults.
"Someone will have information about these attacks and be able to help us remove a very dangerous man from the streets."
Officers were alerted to a series of attacks on women in the E17 area after starting the investigation into Miss Samaraweera's death.
Her body was found in a small play area in Queen's Road park, close to the junction with Markhouse Road. She had been raped and strangled.
Following a review of previously reported sex attacks police were able to use DNA evidence to link three sex assaults, which also happened in Walthamstow in 2009, to her murder.
Five men arrested in connection with the inquiry have all been released without charge.