The 38-year-old father was shot eight times through his car window. A 34-year-old man from Uxbridge was arrested on Wednesday on suspicion of perverting the course of justice.
Police said he was linked to "criminality and drug importation".
A Â£50,000 reward has been offered for information leading to the arrest and prosecution of those responsible.
A man has been arrested over the killing of Redwan El-Ghaidouni who was shot dead on his driveway in Uxbridge.