Two men have been released on bail and two women have been arrested in connection with an attack on a couple in Norwich.
The men, aged 19 and 21 and from the London area, were arrested on suspicion of inflicting grievous bodily harm with intent. They have since been bailed.
Two women, aged 33 and 49, both from Norwich, have been arrested on suspicion of the same offence.
A man, 54, sustained serious head injuries in Rose Lane car park.
His partner, 42, suffered minor injuries.
The man remains in a critical condition at the Norfolk and Norwich University Hospital.
Police have appealed for witnesses to the attack, which happened at about 0130 GMT.