It's a dirty business, but searching a rival's trash is generally legal—as long as it does not involve trespassing on private property or taking the bags before they hit the curb, according to Richard Horowitz, a lawyer who works with Strategic and Competitive Intelligence Professionals, an industry group. In fact, there are best practices associated with Dumpster diving, according to J.J. Gradoni, a private investigator in Houston. Here's how he approaches the matter.

When It's Called For
When big money is at stake or hard evidence is needed for a lawsuit. In one case, an insurance company hired Gradoni to figure out how a lawyer was able to file so many lawsuits based on traffic accidents. Gradoni's staff searched the lawyer's trash, painstakingly reassembled shredded documents, and learned that an insider at the fire department was faxing him accident reports.

Planning the Pickup
Gradoni's first step is to find out when, where, and how often a target's trash gets picked up. An office building's site manager will know this; at a smaller facility, so will many tenants. To avoid attention, Gradoni schedules pickups at night or pays garbage men to deliver the bags. (Though this is technically legal, it can lead to civil litigation.)

Striking Paydirt
Investigators look for invoices, customer lists, bills, faxes, bank statements, and any other documents regarding money changing hands. All provide a window into the day-to-day operations of a company, and most can serve as hard evidence in litigation.

Shredded Material
With a little paste and a lot of patience, it's possible to reassemble documents that have been shredded vertically or horizontally into strips (documents put through crosscut shredders, which effectively turn paper into confetti, are nearly impossible to reassemble).