A man has died and another has been seriously injured in two separate attacks which police are linking.
A 43-year-old man suffered "serious lacerations" to his body in Westbourne Street, Stockton, at 07:15 GMT on Sunday and later died in hospital.
A few hours earlier, a 36-year-old man was taken to hospital with a head injury and cuts after being attacked in neighbouring Yarm Road at 05:45.
Two men have been arrested on suspicion of murder and attempted murder.
The 18 and 39-year-old were arrested on Sunday and both remain in custody.
Two others aged 20 and 29 have also been arrested on suspicion of conspiring to cause grievous bodily harm with intent and are also in custody.