The 36-year-old man was arrested on Friday (May 13) morning, on suspicion of conspiracy to murder and remains in custody.
The latest arrest comes after three dawn arrests more than a year after the killing.
A 41-year-old man, a 29-year-old man and a 34-year-old woman were arrested at around 6am on Wednesday (May 11) for conspiracy to murder and remain in custody at separate London police stations.
A substantial reward of £50,000 reward remains on offer for information leading to the arrest and prosecution of the person or people responsible for the father-of-three 's murder in February 2015.
Detective Chief Inspector Noel McHugh, of the Homicide and Major Crime Command, said: "Extensive enquiries have been carried out over the last year and we have made good inroads into understanding the circumstances surrounding Redwan's murder, leading us to these arrests today.
"Our investigation continues and we are still very much encouraging people to come forward.
"I would like to thank all those who have assisted us so far and I hope the large reward on offer will prompt anyone who has yet to do so to approach us in confidence."
Anyone with any information is asked to call the incident room on 020 8785 8099 or Crimestoppers anonymously on 0800 555111 or via the website .