MINNEAPOLIS (AP) – A statewide takedown of several suspected Native Mob gang members prompted a rare lockdown of Minnesota’s entire prison system, so authorities could ensure that word of the arrests didn’t get out and protect the safety of officers in the field, officials said Wednesday.

A sweeping, 47-count indictment partially unsealed Tuesday and made available Wednesday charges 24 alleged gang members with conspiracy to participate in racketeering and other counts.

The indictment paints a picture of a structured, violent gang that held monthly meetings where members encouraged the assault or murder of their enemies, including rival gang members, government witnesses or anyone who showed disrespect.

It also outlines how the gang monitored the location of its own members and rival gangs in prison, and communicated with incarcerated Native Mob members about their activities.

“These communications furthered the Native Mob’s strength, both in terms of numbers of members, and in its ability to intimidate enemies,” the indictment said.

Six of the defendants – who face charges including attempted murder, assault with a dangerous weapon, and drug charges – were arrested Tuesday in the Minneapolis-St. Paul area, and on the White Earth, Mille Lacs and Leech Lake Indian reservations in northern Minnesota.

But 12 of those charged were already in custody on other charges and had to be re-arrested in prison, U.S. Attorney’s Office spokeswoman Jeanne Cooney said.

Because officials didn’t want inmates to warn those on the outside about possible arrests, all of the state’s 9,500 inmates were confined to their cells from 4 a.m. Tuesday until 5 a.m. Wednesday, and weren’t allowed any phone calls or visitors.

Department of Corrections spokesman John Schadl said it was “very important for the integrity of the operation and the safety of the people in the field that no word get out.”

Six more suspects remained at large Wednesday.

The U.S. Attorney’s Office said the Native Mob is a regional criminal gang that started in Minneapolis in the 1990s and has roughly 200 members, recruited from areas with large numbers of young Native American males. Authorities said its members have been involved in drug trafficking, assault, robbery, murder and drive-by shootings.

The indictment said that since at least the mid-1990s, the defendants and others conspired to commit crimes through the Native Mob, in violation of the federal anti-racketeering law.

The indictment said the Native Mob members were expected to intimidate rival gangs and “use any means necessary to force respect from those who showed disrespect, including acts of intimidation and violence.”

The indictment said the gang members distributed drugs ranging from crack cocaine to ecstasy, supported other gang members financially – including those in prison – shared police reports with each other, and intimidated witnesses.

The indictment said some of the defendants who were incarcerated wrote letters to fellow Native Mob members describing their plans upon release. In one letter, an inmate wrote about the “need to hold people accountable, foes or our own. Discipline and promote fear is the quickest way to progress in our case.”

Another defendant allegedly wrote a letter in 2006, saying he was recruiting new members and holding gang meetings in prison.

The indictment also lists multiple incidents of threats, drive-by shootings, assaults and other crimes. In one 2010 incident, the indictment says, a gang member shot one man three times – while he was holding his 5-year-old daughter.

The indictment also lists incidents in which boiling water was thrown in a victim’s face, and a rival gang member was assaulted with a baseball bat. The indictment also says one defendant threatened to kill Minneapolis police officers who arrested him.

Schadl said that generally speaking, gang members are a threat to a facility’s security because they try to continue their gang activity while in custody.

He said lockdowns are used for many reasons, including to control disturbances and keep order in a facility. Lockdowns of individual living units or single institutions occur a few times each month, but it’s rare to lock down all the prisons at once, he said.

The U.S. Attorney’s Office said about 100 to 150 local, state, federal and tribal law enforcement officers took part in Tuesday’s arrests, after a long-term multiagency investigation.