U.S. Attorney Eileen Decker, right, and FBI Special Agent Joshua Stone appear before reporters outside federal court in Riverside, Calif., Thursday, Feb. 16, 2017, after Enrique Marquez Jr. pleaded guilty to providing the high-powered rifles used to kill 14 people in the San Bernardino terror attack. The judge accepted his plea agreement with prosecutors. Under the plea deal, Marquez could face up to 25 years in prison. A sentencing hearing was scheduled for Aug. 21. (AP Photo/Reed Saxon)

U.S. Attorney Eileen Decker, right, and FBI Special Agent Joshua Stone appear before reporters outside federal court in Riverside, Calif., Thursday, Feb. 16, 2017, after Enrique Marquez Jr. pleaded guilty to providing the high-powered rifles used to kill 14 people in the San Bernardino terror attack. The judge accepted his plea agreement with prosecutors. Under the plea deal, Marquez could face up to 25 years in prison. A sentencing hearing was scheduled for Aug. 21. (AP Photo/Reed Saxon)

RIVERSIDE, Calif. (AP) — A California man who bought high-powered rifles used in the San Bernardino terror attack pleaded guilty on Thursday as the father of one of the victims angrily denounced the plea deal as a “slap on the wrist.”

Enrique Marquez Jr. appeared in federal court in Riverside with his hands cuffed and chained to his waist. He sounded choked up after the prosecutor described what he had done.

Marquez told the judge he had dropped out of high school and college but understood the allegations and the consequences of the plea agreement with prosecutors that could bring him up to 25 years in prison while sparing him a trial.

Gregory Clayborn, the father of one of the people killed, opposed the deal in an impassioned plea to the judge before the hearing.

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“This man supplied these murderers with these weapons and he’s going to get a slap on the wrist, your honor,” Clayborn said, his voice cracking as he described the pain of losing his 27-year-old daughter Sierra.

“My daughter, she didn’t deserve this,” he said.

Marquez was the only person criminally charged in the December 2015 attack that killed 14 people and wounded 22 others at a meeting of San Bernardino County employees. Husband-and-wife assailants Syed Rizwan Farook and Tashfeen Malik were killed in a shootout with authorities later that day.

Marquez is scheduled to be sentenced by U.S. District Judge Jesus G. Bernal on Aug. 21.

In addition to purchasing the weapons, Marquez pleaded guilty to conspiring with Farook to draft earlier mass killing plots targeting a community college and a gridlocked Southern California freeway. Authorities said the pair researched bomb-making and bought materials to make explosives, but never carried out those attacks.

In court Thursday, relatives of victims in the San Bernardino attack were given tissue boxes ahead of the brief hearing. While Marquez was questioned, one sobbed. Another closed her eyes.

Afterward, Clayborn told reporters he believes Marquez knew about the San Bernardino attack.

U.S. attorney Eileen M. Decker said she understands why victims’ relatives may feel the sentence is insufficient due to the pain they have suffered, but explained that she is bound by the law and there is no evidence that Marquez participated in or had advance knowledge of the San Bernardino killings.

But his purchase of the weapons and preparations with Farook for the attacks they never committed laid the foundation for the 2015 assault, she said.

“These chilling plans could have inflicted mass casualties. These plans thankfully were not executed,” she told reporters outside the courthouse. “But there are connections between their planning in 2011 and 2012 that we believe assisted in the horrible attacks that took place in 2015.”

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Prosecutors said Marquez acknowledged being a “straw buyer” when he purchased two AR-15 rifles for Farook that were used years later in the massacre on Farook’s colleagues at the environmental health services division in San Bernardino. Prosecutors have said Marquez agreed to buy the weapons because the pair feared Farook’s Middle Eastern appearance might arouse suspicion.

Marquez also acknowledged plotting with Farook in 2011 and 2012 to attack the community college the pair attended and a Southern California freeway. He said he backed out of the plot after four men in the area were arrested on terrorism charges in late 2012, the FBI has said in court documents.

Marquez and Farook met in 2005 after Marquez moved next door to Farook’s family in Riverside, about 55 miles east of Los Angeles.

Farook began educating his new friend about his Muslim faith and Marquez converted in 2007.

The FBI said the two began discussing extremist views shortly thereafter. By late 2011, Marquez spent time at Farook’s home reading magazines published by al-Qaida and studying radical material online, federal officials said.