Last week, news outlets reported that FBI agents were searching a North Dartmouth, Mass., landfill for a specific piece of evidence related to the Boston Marathon bombing. Though the FBI declined to reveal the nature of that item, an ABC News story suggested that the agents were looking for Tamerlan Tsarnaev’s laptop. The FBI has not revealed whether the search, which wrapped up Friday, was successful. How do you go about finding a specific object in all that garbage?
Painstakingly. The FBI was lucky in that the Crapo Hill Landfill is relatively small, currently a 39-acre operation taking trash from only the nearby Dartmouth and New Bedford communities. (Dzhokhar Tsarnaev was a student at UMass Dartmouth.) A larger, more widely sourced landfill makes searches exceedingly more difficult. Regardless of size, investigators don’t just wade into the filth willy-nilly. Landfills are generally organized by “daily cells,” with one cell filling up before a new one is started, meaning that if you know when a specific load of trash came in, you can narrow down its location on the site. Well-run landfills may also keep detailed records of which trucks dumped their loads in which cells on a given day, further filtering the search. (If the suspect tossed the item in the dump himself at an unknown time or place, his cooperation may be required to make the search worthwhile.) Still, tons of trash can be added in a single day depending on the landfill, so finding a single item requires a combination of persistence, manpower, and luck.
Once investigators know where to look, a team of people—in the Dartmouth case, about 30—don biohazard suits and use rakes, shovels, and similar implements to methodically sort through the debris. Unless the site is composed of entirely organic material, a metal detector would face too much interference to be useful. At Crapo Hill, agents appeared to organize the trash into more manageable rows. Searches usually take a number of days to complete.
While finding evidence in a landfill is extremely difficult, success is not impossible. But the longer an item languishes in the dump, the less likely it is to be found as more trash and layers of covering materials such as dirt are piled on. And even if it is discovered, precipitation and other environmental factors at landfills can quickly degrade evidence.
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Explainer thanks John P. Flannery, former New York federal prosecutor.
Read more on Slate about the Boston Marathon bombing.