A third man has been arrested on suspicion of murdering the brother of two young men who died fighting for Islamist jihadists in Syria.
Abdul Deghayes, 22, was found stabbed in a car in Brighton after a crash on Saturday and died hours later.
A 36-year-old man, from London, was arrested on suspicion of murder at an address in Crawley in the early hours.
Mr Deghayes was a passenger in a VW Polo that collided with other cars. He died as a result of his stab wounds.
He was the twin of Abdullah, 18, and brother of Jaffar, 17, both from Brighton, who were said to have become radicalised and died fighting with Islamists in Syria in 2014.
Mr Deghayes' twin and his younger brother fought for an Al-Qaeda-affiliated jihadist group in Syria, following in the footsteps of their older brother, Amer.
It is believed Amer is still alive in Syria, having left Sussex in 2013.
Ch Insp Andy Bennett said the investigation into Mr Deghayes' death was "still very active and developing".
A woman, 36, from Crawley, was also arrested on Wednesday on suspicion of assisting an offender.
A 54-year-old Brighton man was arrested on Monday and remains in custody.
A 26-year-old man arrested on suspicion of murder on Sunday has been released without charge.
Mr Deghayes died at the Royal Sussex County Hospital following the crash at 21:30 GMT on Saturday near St Joseph's Church, Elm Grove.
Police said there had been a disturbance in Wellington Road, Brighton, where it is believed Mr Deghayes was stabbed.
Mr Deghayes then got into the car, which was driven to Elm Grove before it collided with other vehicles.