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LOS ANGELES — The mother of a man who carried out a 2015 terrorist attack in San Bernardino, California, will plead guilty to destroying a map that was thought to have been drawn by her son to plan the shooting that killed 14 people, federal prosecutors said Tuesday.

Rafia Sultana Shareef, 66, who is also known as Rafia Farook, will plead guilty to alteration, destruction and mutilation of records, the U.S. Attorney's Office for the Central District of California said in a statement.

The charge carries a maximum sentence of 20 years, but the plea deal says prosecutors will recommend a sentence of no more than 18 months.

Syed Farook and Tashfeen Malik arrive in Chicago in July 2014. U.S. government - file

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Shareef's son, Syed Farook, and his wife, Tashfeen Malik, opened fire at the Inland Regional Center in San Bernardino on Dec. 2, 2015, in what authorities have said was a terrorist attack. They were killed in a firefight with police.

Shareef admitted that on the day of the mass shooting, she had told family members that she believed her son and daughter-in-law were responsible, according to the plea agreement.

Before she left the home she shared with them in Redlands, she went to her son's bedroom and fed what appeared to be a map into a shredder, prosecutors said.

"Shareef admitted that she knew her son had produced the document, and she believed it was directly related to his planning of the IRC attack," prosecutors said in Tuesday's statement.

She shredded the document to impede the investigation, the plea agreement says. Prosecutors noted in the document that they have not alleged that Shareef had prior knowledge of the attack.

Shareef is scheduled to make an initial appearance in court March 16, the U.S. attorney's office said. The plea agreement also requires her to cooperate fully with investigators.

When Syed Farook left the home with his wife around 8 a.m. on the day of the attack, he told his mother that they were going to a medical appointment. Instead, they went to the Inland Regional Center and opened fire with what prosecutors have described as high-powered firearms.

Another criminal case is associated with the mass shooting, involving a different person. A man described as a friend of Syed Farook's, Enrique Marquez Jr., was indicted in 2015 on charges that included that he supplied the guns used in the attack.

He is alleged to have acted as a "straw buyer" to get two rifles, prosecutors have said. Nothing in the criminal case alleged that he knew about the attack.

Marquez was to have pleaded guilty in 2017 to two counts, but online court records, some of which are sealed, indicate that last year he moved to withdraw a guilty plea on one of the counts.