Supreme Court judge Paul Coghlan has spent more than 50 years investigating, prosecuting and judging serious crooks on serious crimes.

Coghlan, the grandson of a Chinese merchant, innkeeper and opium dealer, became Director of Public Prosecutions during Melbourne's gangland war, brokering plea deals that cracked the underworld's wall of silence.

From prosecuting a serial killer to pursuing a dodgy detective in one of Australia's first wire tap cases, Coghlan opens up to veteran crime reporter John Silvester in another episode of Naked City.

And a heads-up, there's a language warning for this one.

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