The clearer photograph was taken from a security video of a man seen at Charing Cross station with the killer's last victim, Emanuel Spiteri, three days before his body was discovered in his south-east London flat.
Police also revealed that they are trying to enhance their telephone recording of the suspected killer's voice. The last contact with him was on 15 June.
Detective Superintendent Brian Edwards said: 'We now have a clearer photograph of the man seen in the company of Mr Spiteri. We need to trace that man and interview him as it's obvious he has information that is crucial to the success of this inquiry. 'We're confident anyone who knows that man will be able to recognise him from that photograph. We need to know who is that man and where he is. As far as we are aware he was the last person to see Mr Spiteri alive.'
Police say they still want to contact anyone who may have seen the two men together on the station concourse shortly before Mr Spiteri's body was found in his burnt-out flat in Lewisham last month.
Det Supt Edwards said: 'They were a very distinctive couple. Mr Spiteri was 5ft tall, the other man was over 6ft. They would have stuck out.'
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