With public criminal charges against former Trump campaign chairman Paul Manafort announced Monday morning, this year’s biggest political story—the former FBI director Robert Mueller’s investigation of Russian interference in the 2016 presidential election—enters an important new phase, guided not just by whispers and Twitter wars but by written indictments and the rules of federal evidence.

The indictment targeting Manafort and his business associate Rick Gates—itself a political bombshell—is likely to be merely the first step in a potentially long investigation. Details from the indictment—and other emerging public court documents—will immediately help to shed further light on the tangle of relationships that Manafort and others had with various Russian and Ukrainian contacts in recent years, but there are plenty more investigative avenues that Mueller appears to be following, some far removed from Manafort's orbit.

Manafort faces a long list of charges that includes conspiracy against the United States, conspiracy to launder money, false statements, acting as an unregistered agent as a foreign principal, making misleading statements in violation of the Foreign Agent Registration Act, and seven counts of failing to file reports of foreign bank and financial accounts. That's a dozen in all. Trump campaign adviser George Papadopoulos also pleaded guilty to making false statements, accompanied by a bombshell plea agreement that includes several key details about Russia's alleged attempts to reach out to the Trump campaign.

Here are five rules of federal investigations to keep in mind as you read about the new charges and think about their implications:

1) The FBI takes down whole organizations. The charges announced Monday in Mueller’s investigation are almost assuredly only a first step in what could be an very long and extensive grand jury investigation.

Only rarely does the FBI end up charging a single individual; it’s simply not worth the time and resources of the federal government to go after individuals in cases outside of rare instances, like say, terrorism. Institutionally, the FBI’s modus operandi and DNA is to target and dismantle entire whole criminal organizations—that’s why federal cases usually take so long: The agency starts at the bottom or periphery of an organization and works inward, layer by layer, until it’s in a position to build a rock-solid case against the person at the top.

This investigative method has been the heart of the FBI’s approach since the 1980s, when it and the Justice Department—led by an era of aggressive and brilliant prosecutors like Louis Freeh, Rudolph Giuliani, and Michael Chertoff—began to attack La Cosa Nostra in New York. The FBI relied then on a then-new tool, the Racketeer Influenced and Corrupt Organizations (RICO) Act, to attack and dismantle entire mafia families, charging dozens of suspects in a single case.

The approach, then and now, has almost always been similar: Work on peripheral figures first, encourage them to cooperate with the government against their bosses in exchange for a lighter sentence, and then repeat the process until the circle has closed tightly around the godfather or criminal mastermind. There’s no reason to think that this investigation will be any different.

In fact, members of Mueller’s investigative team cut their teeth on a who’s who of the biggest Justice Department targets of the last quarter century, taking that “organization” approach to cases like Enron (prosecutor Andrew Weissmann led the task force), al-Qaeda (aide Aaron Zebley helped investigate the 1998 embassy bombings before 9/11), and organized crime (prosecutor Greg Andres helped investigate the Bonnano family in New York, as well as the $8 billion Ponzi scheme led by Texan financier Robert Allen Stanford, who’s now serving a 110-year prison sentence).