A father and three of his sons pleaded guilty on the first day of their trial to multiple offences involving thefts from vehicles in Brackley.
James Devlin, 49, and his sons, Noel, 28, Hughie, 26, and Jimmy, 19, all from Dun Roamin Park on Whitfield Road, near Whitfield, were arrested in 2018 on suspicion of conspiracy to steal.
A 16-year-old boy, who cannot be named because of his age, was also arrested.
Detectives investigating the case received 135 reports of thefts from vehicles, mainly sole traders and small businesses, with vans and tools taken from within.
Officers executed two warrants in February 19, 2018, and arrested five suspects who were interviewed in relation to a conspiracy to steal.
All five were charged with conspiracy to steal and were released on police bail while the investigation continued. They were each given strict bail conditions preventing them from entering certain towns and locations.
They attended Northampton Crown Court charged with 35 offences for the first day of a scheduled three week trial on June 27.
James Devlin, Jimmy Devlin and the 16-year-old, all pleaded guilty to the offence of conspiring to steal between September 1, 2017, and February 20, 2018.
Hughie Devlin pleaded guilty to one count of a high value theft. Noel Devlin pleaded guilty to seven counts of theft.
They will next appear at the same court for sentencing on July 18.
Detective Inspector Simon Barnes, who led the investigation, said: “A significant amount of time and resources involving officers and staff, has been dedicated to this investigation in order to secure all of the evidence available that has resulted in the guilty pleas we have seen.
“It is testament to their hard work and that of the Crown Prosecution Service that we have been able to obtain some justice for all of the victims affected by these offenders.
“It cannot be underestimated, the significant impact that these offences have had on individuals and small businesses alike.
“It is not simply the cost of replacing tools, but the loss of income as a result of being unable to work and the extensive repair costs to vehicles, which are substantial.”