The federal racketeering case brought against the violent Mara Salvatrucha gang in Maryland last week is the latest in a string of prosecutions across the country employing a legal weapon originally devised to take down Mafia crime families.

The RICO Act, which stands for Racketeer Influenced and Corrupt Organizations, has been successfully used to prosecute street gangs in Los Angeles, New York, Atlanta and Utah over the past decade. The indictment brought by Maryland U.S. Attorney Rod J. Rosenstein accuses 19 alleged members of the gang, also known as MS-13, of six murders and four attempted murders between April 2003 and June 14. Eight of the 10 attacks occurred in Prince George's County; two were in Montgomery County. The defendants also are accused of conspiring to commit kidnapping, robbery and obstruction of justice.

One element is critical to Rosenstein's case. He must establish that the 19 men are more than a loose confederation of violent criminals but part of an established organization with a hierarchy of leadership and rules.

The indictment offers hints of such an enterprise. It alleges that factions from across the United States meet in person and communicate on cell phones to discuss rules and activities; that dues paid at meetings are used to support members in prison in the United States and El Salvador; and that members are required to commit acts of violence to stay in good standing.

"Where there is proof of structure, organization and leadership, there is fertile ground for RICO prosecution," said Los Angeles Assistant U.S. Attorney Bruce Riordan, the anti-gang and MS-13 coordinator for the U.S. attorney's office in the Central District of California.

Federal racketeering carries a maximum penalty of life in prison. There is no parole in the federal criminal justice system. According to the Justice Department's Criminal Division, about one-third of U.S. attorney's offices filed criminal charges under the RICO statute in 2003 and 2004. It is not clear how many of those dealt with street gangs.

In Los Angeles, Riordan said, his office has prosecuted about 200 gang members over the past 10 years, groups such as the 18th Street Gang, the Mexican Mafia, Aryan Brotherhood and Armenian and Asian gangs.

RICO is not always the statute of choice. Los Angeles gangs such as the Bloods and the Crips, while extremely violent, were not RICO targets because prosecutors could not establish a structure, leadership or business model.

The statute was first used in the 1970s to target violent criminal business operations, such as Mafia crime families. In those cases, the government established organizational hierarchy by probing gambling, money laundering and other activities that generated revenue.

For street gangs, making money is often less important than protecting turf. But territorial zeal can lead to the same kind of organizational pecking order that qualifies as a criminal enterprise under RICO.

"It is crime as business, but not necessarily for financial gain," said Eugene O'Donnell, a professor of law and police science at John Jay College of Criminal Justice in New York and a former police officer and prosecutor who handled organized crime cases.

MS-13 is made up primarily of Salvadoran immigrants, along with other Central Americans and Mexicans. It was formed in the 1980s in Los Angeles, officials have said, initially for protection against older, well-established Mexican gangs. Mara Salvatrucha began showing up in the Washington area in the late 1980s.

In recent months, MS-13 has been accused of a series of attacks in Prince George's and Montgomery and in Northern Virginia. The gang is responsible for more than 20 homicides and dozens of attacks in the Washington area, authorities said. Virtually all the victims have been Latinos.

According to prosecutors and legal scholars, the RICO statute allows federal prosecutors to cast a wide net in connecting gang members to crimes and in introducing evidence in court, something that is more restricted in state court.

For example, in a RICO trial, prosecutors can implicate defendants in murders for which they have not been charged. Some defense lawyers object to the slackening of such rules, arguing that the net cast by RICO is unjustly large, demonizing defendants and tarnishing them for their association.

"They say the nature of the prosecution is too suggestive," said O'Donnell, characterizing the complaints of the criminal bar. "If you throw so much mud, you only have to make some of it stick."

Prosecutors say RICO, which has been upheld by courts across the country, is invaluable for targeting gang leaders.

"The leaders are the shot callers of the gang. They call the shots; they don't shoot the shots," Riordan said. "They may not physically lay their hands on anybody, and they think if they don't pull the trigger, they are insulated. RICO allows us to get at the leadership of a gang."

Riordan said that because RICO trials generally involve several defendants, the cases are labor intensive and can take two to four years to prosecute.

He said it would be foolish for prosecutors to try to force the RICO statute to apply to a case.

"That commitment of time is so extraordinary. It is a serious and sincere commitment of your resources and your life," he said. "You better use it where it fits."

Maryland U.S. Attorney Rod J. Rosenstein announces the indictment on federal racketeering charges of 19 alleged MS-13 members Thursday.