His death is one of five that may be linked to disorder across England.
A 26-year-old was arrested in Mitcham. A 24-year-old was arrested in Brighton and later released on bail.
Two men were arrested at the scene on suspicion of handling stolen goods. They were later bailed pending further inquiries.
Car chase Mr Ellis is one of five people whose deaths police believe may be linked to the recent disorder across England, sparked by the death of Mark Duggan last Thursday in Tottenham.
Initial inquiries suggest that Mr Ellis had travelled to the Croydon area with friends.
It is believed the group became involved in an altercation with a group of approximately nine individuals.
This culminated in a car chase involving three vehicles, which started in Scarbrook Road, Croydon, passing along the A232 flyover into Duppas Hill Road, where Mr Ellis was shot.
A post-mortem examination showed he died from a gunshot wound to the head.