Federal prosecutors said Tuesday the white supremacist Aryan Brotherhood maintained its reputation as one of America's most notorious prison gangs by murdering rivals and its own members who violated gang rules.

During closing arguments in the trial of four suspected gang ringleaders, Assistant U.S. Attorney Terri Flynn said the group was ruthless and relentless in running a criminal operation in prison and on the streets.

"The Aryan Brotherhood is a violent, murderous prison gang," Flynn said. "They killed all those who threatened the criminal enterprise."

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On trial are Barry "The Baron" Mills, Tyler "The Hulk" Bingham, Edgar "The Snail" Hevle and Christopher Overton Gibson. They are accused of orchestrating 32 murders and attempted murders involving the gang that was founded in 1964 at California's San Quentin prison.

The government is pursuing the case under a federal racketeering law originally passed to target organized crime.

It is believed to be one of the largest death penalty cases in U.S. history. Of the 40 people originally arrested, up to 16 could face the death penalty in several trials.

Closing arguments by both sides in the current case were expected to last until Friday.

On Tuesday, prosecutors showed jurors written messages from gang members and photos of people they contend were killed at the behest of gang leaders.

Flynn said the gang recruited the most violent inmates at high-security prisons who would protect the gang at any cost.

"Even its own members weren't safe," she said.

During the trial, which began four months ago, prosecutors called to the witness stand convicted killers, former gang members and jailhouse informants who testified about the violent tactics of the gang.

Defense lawyers countered that the aging defendants were forced to join the gang simply to survive in the tough prison environment. Testimony against them was manufactured and paid for with money and prison privileges, according to the defense.

Flynn denied those accusations.

"We need cooperators to infiltrate a gang like this," she said.

Nearly all of the witnesses have been former members of the Aryan Brotherhood. Their gruesome testimony revealed the dark world of prison life and gang membership.

Jurors heard accounts of dozens of murders and attempted murders, including one in which the attacker licked the dead man's blood from his hands while laughing hysterically.

The trial also provided a look at gang practices of sending messages in invisible ink made from urine and using runners to smuggle knives and drugs in their rectums or genitals when they visited.

Federal prosecutors say Mills and Bingham ordered a 1997 race war at a prison in Lewisburg, Pennsylvania, that led to the deaths of two black inmates.

Defense attorneys countered with the testimony of two black prison gang members who said the Aryan Brotherhood was too small and weak to attack a rival black gang behind bars and incite a race war.

The trial stemmed from a six-year investigation that culminated with arrests in 2002. Nineteen suspects struck plea bargains and one died. Two more trials are scheduled for this fall in Los Angeles.

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