Essex Police have also named all four victims
A lorry and a minibus collided between Junctions 27 and 26 just after 6.15pm on Monday, 23 August.
The three victims who died at the scene have been identified as 31-year-old Abigael Muamba from Edmonton Green, 60-year-old Dexter Augustus from Waltham Forest and 59-year-old Jennifer Smith from Stratford.
Lisa Gardiner, 44, from Walthamstow, has since died of her injuries in hospital.
All of the victims had been passengers on the minibus.
Two men were arrested on the evening of the incident, the minibus driver and a lorry driver.
The minibus driver has since been de-arrested following new information.
The lorry driver, a 64-year-old man from Ipswich, was arrested on suspicion of causing death and serious injury by dangerous driving and driving while unfit through drink or drugs.
Inspector Mark Fraser, who leads Essex Police’s Serious Collision Investigation Unit, said:
“Our thoughts are with the families and loved ones of those who lost their lives in this awful incident.
“My officers are working tirelessly to try and piece up what led to the collision.”
Anyone who witnessed the collision or has dashcam footage or any information has been asked to come forward.
You can also call 101 and cite incident 972 of Monday 23 August.
Information can also be given to independent charity Crimestoppers anonymously on 0800 555 111.
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