Hugo Pinell, the last jailed member of the “San Quentin Six,” who were the victims of a frame-up carried out more than 40 years ago, was murdered August 12 at California State Prison, Sacramento, a maximum-security prison adjacent to the notorious Folsom State Prison. Officials allege that two inmates stabbed Pinell, 71, at approximately 12:55 p.m. He quickly succumbed to his wounds and was pronounced dead at 1:22 p.m.

The attack sparked a riot involving some 70 inmates. Prison guards engulfed the area with pepper spray, fired roughly 160 rounds from less-than-lethal munitions and three warning shots from an M-14 rifle.

In total, 29 inmates were injured, with 18 treated at the prison’s medical center. Eleven others were taken to outside hospitals for treatment of stab and puncture wounds, broken bones, head trauma and other serious injuries. One remains in critical condition suffering from a severe head injury and multiple stab wounds.

Pinell was the longest-serving inmate in prison isolation units in California’s history until being released into the general prison population on July 29. He had spent more than 43 years in solitary confinement, and had been denied parole 10 times before his death, most recently in May 2014.

His family and his attorney, Keith Wattley, assert that prison officials knew that Pinell would be targeted for murder due to his history. “He has been a target from just about every group in prison because of his notoriety and what he did years ago,” Wattley said after the killing. “This was foreseeable, which is what makes it so much worse and why the family is looking for answers as to why prison officials let this happen.”

The killing of Pinell has all the hallmarks of a politically motivated state murder. The circumstances are highly suspicious: given his sudden entry into the general population, prisoners would only have known he was going to be in the exercise yard on August 12 if they were tipped by the guards. Social media lit up afterward with guards celebrating his death.

The date of the stabbing was also significant: August 12, 2015—39 years to the day after Pinell’s conviction as one of the San Quentin Six. It also came three years after the August 12, 2012, agreement between representatives of white, black and Hispanic prisoners to call a halt to interracial violence among prisoners, which Pinell contributed to.

A Nicaraguan immigrant who came to California at the age of 12, Pinell was charged with rape in 1964 after a sexual encounter he claimed was consensual. He pleaded guilty with the understanding that he would be eligible for parole in six months. Instead, the 19-year-old was given a sentence of three years to life.

In 1971, in the seventh year of this sentence, he was charged as one of the San Quentin Six, on frame-up charges stemming from an alleged prison break in which prison guards murdered George Jackson, the most prominent prison recruit to the Black Panther Party. Jackson’s writings, including Blood in My Eye and Soledad Brother, won him an international audience, as well as the undying hatred of the California political establishment and its massive army of corrections officers .

Three of the six were convicted in 1976, after the longest trial in state history up to that time. The jury was kept deliberating for 24 days, also a record, before eventually returning guilty verdicts on only 6 of the 46 charges brought against the prisoners.

Pinell’s ordeal was torture by another name: he was imprisoned for 50 years, of which 43 were served in solitary confinement, including 24 years, from 1990 to 2014, at the notorious SHU at Pelican Bay.

Pinell was the sole member of the San Quentin Six still in prison. Alongside Pinell, Johnny Larry Spain and David Johnson were also convicted, while Willie Tate, Fleeta Drumgo and Luis Talamantez were all acquitted. Spain was released on parole in 1991 and Johnson in 1993.

As the Bulletin, the US forerunner to the World Socialist Web Site, wrote at the time of the trial, “The six men were picked out because they had been active in prison political organizing, had denounced police murders inside the prison, or had refused to turn informer.”

The trial, which lasted 507 days, covered 20,000 pages of testimony and cost over $2 million, demonstrated the lengths to which the government would go to cover up the police conspiracy to kill Jackson.

Jackson was first imprisoned at age 18 in 1960, after being arrested for an alleged robbery of $71 from a gas station. When promised a short term in jail, Jackson pled guilty. He was sentenced to one year to life under California’s reactionary sentencing laws, and was repeatedly kept in prison as he began to espouse radical politics. At the time of his murder, he was in his 12th year of imprisonment.

While in Soledad Prison, Jackson joined the Black Panther Party and wrote his two widely popular books, prompting prison officials to declare him a “dangerous freewheeling convict leader who must be isolated because of his impact on the prison population.”

Shortly thereafter, Jackson, Fleeta Drumgo and John Clutchette were indicted on trumped-up charges of murdering a prison guard. The three became known as the Soledad Brothers and gained notoriety when Angela Davis, a leading member of the Communist Party, headed their defense campaign.

In August 1970, Jackson’s brother, Jonathan Jackson, was set up by a member of the Criminal Conspiracy Section (CCS) of the Los Angeles Police Department. Black Panther leader Melvin Smith (in reality a CCS agent) promised Jonathan Jackson that there would be a getaway car with eight Panthers outside the Marin County court where prison inmate James McClain was undergoing trial, as part of plans to free a number of prisoners, including George Jackson. However, on the day of the trial, Smith told Jonathan Jackson that the eight Panthers had found the court too well guarded, and left.

Jonathan Jackson chose to mount a desperate attempt by himself to free the prisoners and take hostages to trade for his brother and the other Soledad prisoners, entering the courtroom with a bag containing pistols and a sawed-off shotgun. He armed McClain and two trial witnesses, inmates William Christmas and Ruchell Magee, and took the judge, prosecutor and three jurors hostage.

When they tried to flee in a county van, local cops and San Quentin guards cut them down with a hail of bullets, killing Jonathan Jackson, Judge Haley, McClain and Christmas. Two other members of the CCS, who inexplicably flew to Marin that day to attend the trial, helped police riddle the vehicle with bullets.

Davis was accused of assisting in the purchase of the weapons used by Jackson.

A year later, George Jackson was shot and killed by prison guards in the yard at San Quentin, in a police-provoked escape attempt used to justify his murder. Prison officials claimed that Jackson tried to escape after obtaining a gun from an attorney, Stephen Bingham, yet inmate witnesses claim that there was no gun or escape attempt. Affidavits from the trial revealed that state prison authorities were responsible for delivering a defective gun and window putty labeled as plastic explosive to Jackson. Bingham was later acquitted in 1984 of charges related to Jackson’s alleged escape attempt.

The subsequent frame-up trial of the “San Quentin Six” was a travesty of justice that sought to make an example of the prisoners in the aftermath of the 1971 Attica, New York, uprising, which was itself in part a response to the police murder of George Jackson a month earlier.

At each court hearing, the defendants were chained hand and foot in a blatant attempt to manipulate the jury. The six men were secretly beaten and brutalized by guards, undergoing torture-like conditions at the San Quentin Adjustment Center, the maximum-security section of the notorious San Quentin prison complex.

Ultimately, two of the six defendants, Pinell and David Johnson, were acquitted of murder and conspiracy charges but convicted of assault on a prison guard. Both were already life-sentence inmates, which meant that this felony carried an additional life imprisonment sentence. Spain was the only defendant convicted of conspiracy and murder.

Of the 12 men involved in the three cases linked to George Jackson, two were killed in prison 44 years apart, Jackson and Pinell, and three, Jonathan Jackson, William Christmas and James McClain, died in the Marin County Courthouse bloodbath. Tate, Drumgo, Talamantez, Spain and Johnson have been released. John Clutchette, one of the three Soledad brothers, and Ruchell Magee, the only survivor of Marin County, remain in prison to this day, more than 45 years after the events.

Clutchette has been found suitable for parole in 1972, in 2003 and in 2015, but remains in prison because Democratic Governor Jerry Brown reversed the most recent recommendation of the parole board. Clutchette turns 72 this year, but the machinery of capitalist injustice remains implacable.

Ruchell Magee is even older, turning 75 this year. He remains in prison, from his conviction on charges related to the Marin County Courthouse shootings. He was abandoned by his co-defendant, Stalinist celebrity Angela Davis, and the Communist Party USA, who severed her case from his to obtain a more favorable legal setting for her own trial, which ended in acquittal. The Stalinists refused to lift a finger to defend Magee, who ultimately received a sentence of life without parole.