A recent article in the Washington Post discussed the relationship between computer repair technicians at Best Buy's Geek Squad, and law enforcement.  

Law enforcement is prohibited from performing searches of citizens computers without "probable cause" that a crime has been committed, and the issuance of a search warrant for the seizure and inspection of that computer.  However, private citizens can perform searches without warrants.  

For instance, a roommate could inspect the shared computer of another roommate looking for a document that she left on it, and upon searching it, could encounter videos of child pornography.  She would be justified in reporting this to law enforcement, who could then apply for a legal search warrant allowing them to search the computer and use what they find as evidence.  They would be allowed to incorporate the observations of the roommate, regarding what she observed saved on the computer, in their search warrant application.

The lines are blurred considerably if law enforcement is behind the citizens search.  Such a search could be considered a "government action" and thus be prohibited absent a search warrant.  

According to lawyers for a California doctor charged with possession of child pornography:

Technicians for Best Buy's “Geek Squad City” computer repair facility had a long, close relationship with the FBI in “a joint venture to ferret out child porn,” according to claims in new federal court documents, which also note that Best Buy's management “was aware that its supervisory personnel were being paid by the FBI” and that its technicians were developing a program to find child pornography with the FBI's guidance.

Defense attorneys for the doctor, stated in court filings he said that there were “eight FBI informants at Geek Squad City” between 2007 and 2012, and that the facility's “data recovery system was designed to identify and report child porn from all over the country.” A number of Geek Squad employees received $500 or $1,000 payments from the FBI, documents and testimony showed. Riddet cited an FBI letter to the U.S. attorney in Kentucky which stated that, “Under the control and direction of the FBI, the CW [confidential witness] agreed to notify the FBI when CW detects the presence of child pornography during the regular course of CW's employment and is willing to testify in a court of law.”

If the court finds that the employees of Best Buy were also government agents, it is likely that the evidence derived from the illegal searches will be suppressed, and the case dismissed.  

If you have been charged with a crime due to the discovery of something at Best Buy, you should contact the criminal defense law firm of Newton & Hall, for a confidential consultation.