Agents paid managers in the retailer's device repair unit to pass along information about illegal content discovered on customers' devices, according to documents posted online by the Electronic Frontier Foundation. The digital rights group sued the FBI for the documents last year after the bureau denied a Freedom of Information Act request.
The EFF filed the lawsuit to learn the extent to which the agency trains and directs Best Buy Geek Squad employees to conduct warrantless searches of customers' devices during maintenance. The EFF said it was concerned that use of repair technicians to root out evidence of criminal behavior circumvents people's constitutional rights.
What the EFF found was that the agency's relationship with Geek Squad employees goes back at least a decade. An FBI memo from 2008 describes a meeting between Best Buy employees and the agency's "Cyber Working Group" at the company's Kentucky repair facility.
The memo describes how Best Buy employees gave agents a tour of the facility and went on to say the bureau's Louisville Division "has maintained close liaison with the Geek Squad's management in an effort to glean case initiations and to support the division's Computer Intrusion and Cyber Crime programs."
Another document shows the FBI approved a $500 payment to a "confidential human source" whose name was redacted. The EFF said the payment appears to be one of many connected to the prosecution of Mark Rettenmaier, a Southern California doctor accused of possessing child pornography after he sent in his computer to Best Buy for repairs.
The EFF said the documents detail investigation procedures in which Geek Squad employees would contact the FBI after finding what they believed to be child pornography on a customer's device.
The EFF said an FBI agent would examine the device to determine whether there was illegal content present, and if so, seize the device and send it to the FBI field office closest to where the customer lived. Agents would then investigate further, and in some cases try to obtain a warrant to search the device.
Best Buy said last year that three of the four employees who may have received payment from the FBI are no longer employed by the company. The fourth was reprimanded and reassigned.
Best Buy didn't immediately respond to a request for comment but told CNET sister site ZDNet that Geek Squad employees inadvertently discover suspected child pornography on customers' computers nearly 100 times a year.
"We have a moral and, in more than 20 states, a legal obligation to report these findings to law enforcement," Best Buy said in a statement. "We share this policy with our customers in writing before we begin any repair.
"As a company, we have not sought or received training from law enforcement in how to search for child pornography. Our policies prohibit employees from doing anything other than what is necessary to solve the customer's problem. In the wake of these allegations, we have redoubled our efforts to train employees on what to do -- and not do -- in these circumstances."