The Supreme Court agreed Monday to decide if police may prosecute new crimes with evidence seized from homes of criminals who consented to blanket searches as a condition of probation. 

The Justice Department and California's attorney general both asked the justices to reconsider lower court rulings that threw out bombmaking supplies other evidence seized during the search of a home of a man on probation for an unrelated drug crime. 

At issue is the rationale for searches of probationers' homes, and whether a probationer waives constitutional protections by giving advance consent to a search. 

The case concerns a northern California man suspected of a series of vandalism attacks on Pacific Gas & Electric transformers and other property. 

Mark James Knights had a long history with the utility, which had accused him of stealing electric service and running out on his bill. 

As a condition of probation for a drug conviction in 1998, Knights agreed to let police or probation officers search him, his home, car or other property at will. 

Sometimes called a "Fourth waiver," the form Knights signed greatly limits his Fourth Amendment protection against unreasonable search or seizure. 

Knights contended police used his probationer status as a pretext to follow a hunch that he and a friend were behind an explosion and fire that damaged a PG&E transformer. The explosion knocked out telephone service to the Napa County Airport. 

The early morning search of Knights' apartment was intended only to investigate the fire, and not to check up on Knights' rehabilitation for the drug conviction, he argued. 

Police watched the pair for two days after the fire, and then went into Knights' apartment without a warrant. There, they found detonation cord, ammunition, liquid chemicals, books on chemistry and electric circuitry, bolt cutters and a brass padlock stamped "PG&E." Police also said they found drug paraphernalia. 

Knights was arrested and charged with arson conspiracy and other crimes. 

A federal judge ruled that evidence seized at the apartment could not be used at trial, and the San Francisco-based 9th U.S. Circuit Court of Appeals agreed. 

Knights did consent to searches when he agreed to terms of his probation, the appeals court found. 

"But we have made it clear that this consent must be seen as limited to probation searches, and must stop short of investigation searches," the court found. 

The 9th Circuit, which has issued similar rulings before, is at odds with the California Supreme Court over the legitimacy of this kind of probation search. 

Two other states, Arkansas and Georgia, have rules similar to California's, according to a survey by the Rutherford Institute. The generally conservative legal group filed a friend-of-the-court brief on Knights' behalf. 

Other states require police or probation officers to meet specific conditions before they can search probationers' homes.