The DPP should bring this case to trial post haste. With these murders occurring in 2005 and 2006, there should be sufficient opportunities already to accumulate the evidence against Khan especially since he was incarcerated for most of that time lending comfort to others feeling safe enough to say what they know about Khan's alleged involvement in these murders.
Most cases remain cold due to the inability to identify a perpetrator. Given that Khan was regarded as the mastermind for more than a decade, this should be easy to bring to judgement.