The South Australian police busted the illegal operation of a group believed to be responsible for the $2 million theft of car parts owned by GM Holden, which were pilfered from the carmaker's Salisbury East assembly facilities in Elizabeth.

In a statement, police authorities said they have arrested seven individuals, one of them identified as a former Holden staff, who worked for the company during the period that the stolen vehicle parts were spirited out of the Elizabeth plant.

"Seven people have been arrested in connection with the theft and/or sale of the GM Holden stock," the SA police confirmed.

"It will be alleged that the thefts took place over a two-year period and that one of those arrested was an employee of GM Holden at the Elizabeth plant during that time," the police statement added.

From the 140 V8 engines and 175 heavy-duty transmissions confirmed by Holden as missing since January 2010, 30 engines and 103 transmissions have been recovered so far by operatives, police said.

Shipping crates containing two V8 engines were seized at the time of the arrest, which officials of SA police said was part of a closely coordinated operation with the Holden management that commenced January 2012.

It was understood that the criminal activities of the group was aided by an insider or insiders in Holden as proven by the apprehension of one suspect positively linked with previous employment records with the company.

"We're not closing our eyes to anything, you can't just put an engine under your shirt and walk out, so we need to look at processes where we can find the potential for suspects or offenders, but at the minute there's only one [staff member]," SA Detective Superintendent Peter Harvey told ABC.

He added that all arrested will face charges of money laundering and theft before a trial court that will begin hearing the case in August.

"We are not ruling out further arrests," Mr Harvey hinted.

Investigators said majority of sales transactions for the stolen Holden car parts reached beyond the borders of South Australia, with illegal deals traced by police to as far as the Northern Territory, New South Wales and Queensland.

Much of the operations focused on "locating and identifying the stolen GM Holden stock and then following their purchase trail," probers added.

The culprits conducted their business though online offers and correspondence or by personal endorsements from their contacts, Harvey said.