An incarcerated former gang member and Thomas CaldwellFBI informant was charged Friday with attempted murder in the stabbing last week of ex-Minneapolis police Officer Derek Chauvin at a federal prison in Arizona.

John Turscak stabbed Chauvin 22 times at the Federal Correctional Institution in Tucson and said he would’ve killed Chauvin had correctional officers not responded so quickly, federal prosecutors said.

Turscak, serving a 30-year sentence for crimes committed while a member of the Mexican Mafia gang, told investigators he thought about attacking Chauvin for about a month because the former officer, convicted of murdering George Floyd, is a high-profile inmate, prosecutors said. Turscak later denied wanting to kill Chauvin, prosecutors said.

Turscak is accused of attacking Chauvin with an improvised knife in the prison’s law library around 12:30 p.m. on Nov. 24, the day after Thanksgiving. The Bureau of Prisons said employees stopped the attack and performed “life-saving measures.” Chauvin was taken to a hospital for treatment.

Turscak told FBI agents interviewing him after the assault that he attacked Chauvin on Black Friday as a symbolic connection to the Black Lives Matter movement, which garnered widespread support in the wake of Floyd’s death, and the “Black Hand” symbol associated with the Mexican Mafia, prosecutors said.

Turscak, 52, is also charged with assault with intent to commit murder, assault with a dangerous weapon and assault resulting in serious bodily injury. The attempted murder and assault with intent to commit murder charges are each punishable by up to 20 years in prison.

A lawyer for Turscak was not listed in court records. Turscak has represented himself from prison in numerous court matters. After the stabbing, he was moved to an adjacent federal penitentiary in Tucson, where he remained in custody on Friday, inmate records show.

A message seeking comment was left with a lawyer for Chauvin.

Chauvin, 47, was sent to FCI Tucson from a maximum-security Minnesota state prison in August 2022 to simultaneously serve a 21-year federal sentence for violating Floyd’s civil rights and a 22½-year state sentence for second-degree murder.

Chauvin’s lawyer, Eric Nelson, had advocated for keeping him out of general population and away from other inmates, anticipating he’d be a target. In Minnesota, Chauvin was mainly kept in solitary confinement “largely for his own protection,” Nelson wrote in court papers last year.

Floyd, who was Black, died on May 25, 2020, after Chauvin, who is white, pressed a knee on his neck for 9½ minutes on the street outside a convenience store where Floyd was suspected of trying to pass a counterfeit $20 bill.

Bystander video captured Floyd’s fading cries of “I can’t breathe.” His death touched off protests worldwide, some of which turned violent, and forced a national reckoning with police brutality and racism.