Azezur Khan, known as Ronnie, had just left the service of his school friend in East Dulwich and was making his way to the burial when he was gunned down at around 3pm.
The Metropolitan Police said he was hit a number of times in an exchange of gunfire between Rocknells Place and Forest Hill Road.
A fresh appeal comes just days before the second anniversary of his death on November 3.
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Scotland Yard said two murder investigations have been launched following the separate incidents, which both happened in the past week.
Photos show the extraordinary surgical procedures to remove the growth.
The Met Police says 143 firearms have been handed in at stations across the capital in just seven days, including two antique machine guns.