DENVER, Colorado (CNN) -- Twenty alleged members of a Hispanic gang believed to be one of the nation's largest and most violent have been indicted in Colorado on drug and firearm charges, authorities said Tuesday.

This grafitti in North Denver is the work of the gang MS-13, the Department of Justice says.

Of the 20 alleged MS-13 members named in two indictments, eight were arrested Tuesday morning in Denver and in Los Angeles, California, authorities said. Another eight were already in custody, according to a news release from the U.S. Attorney's Office for the District of Colorado.

Four remain at large, the office said.

"The arrests were the culmination of a three-year investigation into one of the most notorious street gangs in the country," the release said.

Jeff Dorschner, spokesman for the U.S. attorney's office, said the indictments stemmed from a multiple-agency and multiple-state effort.

Some of the defendants are accused of drug dealing activity that prosecutors said reached all the way into a California prison. In the course of the investigation, police seized 10 pounds of methamphetamine, 2.3 kilograms (5 pounds) of cocaine, a small amount of heroin, 12 firearms and $3,300 in cash, according to the release.

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Police said they believe the gang members "conspired to distribute, and possessed with intent to distribute, quantities of methamphetamine, cocaine, heroin and marijuana," federal prosecutors said.

"The conspiracy, and other related drug distribution charges included the distribution of the illicit drugs on the streets of metro Denver, as well as in a facility in California called the High Desert State Prison."

Other defendants are charged with illegal firearm possession, authorities said.

Nine defendants in addition to the 20 named in federal indictments are being prosecuted in Colorado state court, according to federal prosecutors.

The defendants face maximum sentences of life in prison, depending on the offense, as well as fines up to $2 million, authorities said in the news release.

MS-13 has long been regarded by law enforcement agencies as one of the deadliest gangs in the United States and beyond. It is estimated to have up to 50,000 members worldwide, about 10,000 of whom are believed to be active in at least 38 states, according to an attorney general's report to Congress on gangs in April 2008. In 2004, the FBI created a task force to focus on MS-13.

Federal authorities have said that most MS-13 members are immigrants from El Salvador or the children of Salvadoran immigrants. The gang originated in Los Angeles, authorities have said, and it has spread across the United States and into Mexico, Honduras, Guatemala and El Salvador.

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