The inmates -- Jose Sablan, 43, and James Guerrero, 40 -- were indicted earlier in August and charged with murder. They have not yet entered a plea.
"It was two against one, you know, and no one helped him," said Rivera's grieving mother, Terry. "I didn't think that it would happen, but it was not safe for him to work there."
Rivera was 22 and had been in his job at the 960-plus inmate prison for just 10 months when he died.
He was alone guarding about 100 inmates at the time of the attack and had a radio to call for backup in case of trouble. He didn't have what many guards in California's state prisons routinely count on: pepper spray, a protective vest and a collapsible baton.
Federal officers are not allowed to have those items.
CNN asked the federal Bureau of Prisons why it opposes giving its corrections officers nonlethal weapons. In a statement, the bureau said the issue is under review and no final decisions have been made.
"However," the bureau added, "we also know through 75 years of experience that federal correctional facilities are managed most effectively through frequent and direct communication with inmates."
Rivera's death has generated support for more protective gear and nonlethal weapons for federal corrections officers and has brought nationwide attention to the threats facing them, said guards and their union officials.
One officer who has worked for several years at Atwater, where Rivera was killed, said he feels threatened every day. Unless the federal government provides additional protection, he said he's thinking about leaving the job.
The officer requested his name not be used because he fears retaliation. He recounted how a fellow corrections officer's jaw was broken in nine places in an inmate attack last year.
"Every single inmate in there is armed to the teeth for his own protection," the officer said. "I am not Bruce Lee, so I can't take on 110 inmates by myself.... Every day it is like David vs. Goliath. You are taking on the world by yourself."
Prisoners make shanks like the one used to kill Rivera and other weapons from otherwise benign objects -- toothbrushes, toilet parts and kitchen utensils to name a few. Gang rivalries exacerbate an already volatile situation.
Gearing up isn't the only solution, said union officials who represent the federal prison system's 15,427 officers. The American Federation of Government Employees said the federal prisons are severely overcrowded and understaffed. On average, they are at 136 percent of capacity.
"The homicide rates among the inmate populations are at the highest levels they've ever been in the history of the Bureau of Prisons," said Bryan Lowry, the president of the union's prison councils. "The assaults on staff, whether weapons or no weapons, has intensified," he added
More officers are needed to ensure safety in the federal prisons, which house 165,000 inmates, the union said.
The Bureau of Prisons said 14 percent of its jobs are unfilled at its 114 prisons and there is an "urgent need" for officers at several of the high security penitentiaries.
It is taking specific action at Atwater by offering a 17 percent recruitment incentive for new hires.
But the bureau disputed that violence toward guards is on the rise.
Federal officials said the rate of "serious assaults" on staff at penitentiaries has not increased over the past several years. But they said inmate assaults on both staff and fellow prisoners are more severe.
While not agreeing to provide officers with pepper spay or batons, the bureau said it has reviewed operations at 12 high-security prisons and is making some changes. The agency said it will buy protective vests and divide inmates into smaller groups when they are being moved. Two staff members will be added to beef up supervision at the prison housing units.
"The safety and security of our staff continues to be the highest priority of the Bureau of Prisons," the bureau said in its statement. It refused an interview request.
Officials in California's state prison system opened their doors for a CNN crew and talked openly about the nonlethal weapons and other protective gear that have become standard issue.
In the state prisons, each guard wears a stab-resistant vest and carries a can of pepper spray and an expandable baton. Officers said they would feel completely vulnerable if they didn't have them.
"The population is just too unpredictable and you never know if they are going to turn on you or not," said James Walker, warden at the California State Prison-Sacramento.
At that institution, more than 3,000 prisoners are housed in sections depending on their history of violence, whether they have any mental health problems or have posed any danger while incarcerated.
Prison officials said the pepper spray is used several times a week to quell incidents, while officers use their batons at least a few times a month.