A 22-year-old man (arrested on suspicion of murder) and a 34-year-old woman (arrested on suspicion of assisting an offender) were bailed until June.
A 20-year-old man (arrested on suspicion of murder) remains in custody.
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The expansion of the probe came as Jeremy Corbyn declared Carillion's demise a "watershed moment" that should end "rip-off privatisation".
Tuesday afternoon's weather for the west of the region
Tuesday afternoon's weather for the east of the region