The white supremacist group, the Aryan Brotherhood, is said to have controlled a network of US jails for decades.
Witness Clifford Smith told the court the gang used violence to keep power.
Prosecutors are seeking the death penalty for two of the suspects, Barry Mills, 57, and Tyler Davis Bingham, 58. All four deny charges of murder.
The trial in Santa Ana, California, is the first in a series aimed at breaking the Aryan Brotherhood’s influence.
Formed in 1967 in California’s San Quentin prison, the gang is accused of running drug trafficking rings through a network of jails and accepting murder contracts from organisations like the mafia.
Source: BBC News
