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Twelve people have been arrested by officers investigating the events leading up to the crash on the A66 which killed seven people, including two police officers.
Some of those held over the A66 investigation are suspected of “participating in the activities of an organised crime group” Cleveland Police said, adding that four of those killed in the car which hit the police vehicle had previous police convictions.
Police said nine men and three women, aged between 19 and 61, were arrested over alleged criminality leading up to the collision for offences include possession of a firearm and participating in the activities of an organised crime group.
The force said on the morning of the collision, it received several reports of two vehicles being driven dangerously.
The first vehicle, believed to be a Volvo XC60, was witnessed ramming properties in the Middlesbrough area.
The second vehicle, a Volkswagen Passat, is believed to have been associated with the activities of the Volvo.
Police said both vehicles were operating with cloned number plates but were picked up by automated number plate recognition technology.
The Volvo XC60 involved in the initial reports has been traced and recovered in Middlesbrough.
Pc Matthew Blades, 37, and Pc Tom Clough, 38, were killed when the Volkswagen Passat, that had been pursued by police and was driving the wrong way on a dual carriageway, hit their marked armed response vehicle.
Cole Robert Worthy, 17, Theo Rae, 17, Makai Saddington, 18, and 23-year-olds Michael Robert Cahill and Jacob Matusiak were also pronounced dead at the scene near Middlesbrough early on Saturday.
The crash in Teesside took place 10 seconds after a pursuit by other officers was terminated.
Four of the five people in the Passat, including three teenagers, had previous police convictions, Cleveland Police said.
Pc Blades and Pc Clough were not involved in the original pursuit, but had been called to the area to assist with the search for the Passat.
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