The mother of the San Bernardino attacker who carried out a 2015 terrorist plot that killed 14 people at a California Christmas party will plead guilty later this month to destroying a map that was allegedly drawn by her son to plan the shooting.

Rafia Sultana Shareef, 66, 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 Tuesday. The charge against Shareef carries a maximum sentence of 20 years, but a plea deal she struck with prosecutors will seek a sentence of no more than 18 months behind bars.

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On the day of the mass shooting, Shareef told family members she believed her son, Sayed Farook, and his wife, Tashfeen Malik, were responsible for the grisly killings at the Inland Regional Center. Before she left the home she shared with the couple, Shareef went into her son's room and fed what looked like contents of a map into a shredder, prosecutors claim.

"Shareef admitted that she knew her son had produced the documents, and she believed it was directly related to his planning on the IRC attack," her plea agreement claims.

Farook and Malik opened fire at the IRC in San Bernardino on Dec. 2, 2015, in what authorities described as a terrorist attack. The couple was killed in a firefight with police.

Shareef will make an initial court appearance on March 16.

According to prosecutors, her plea agreement also requires her to fully cooperate with authorities.

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Not only did her son and his wife kill 14 people but an additional 22 were wounded.

On the morning of the attack, Farook and Malik allegedly told Shareef that they were going to a medical appointment, but ended up opening fire at a Christmas party for employees, prosecutors said.

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Another person indicted in the case is Farook's friend Enrique Marquez Jr. Investigators claim Marquez Jr. supplied the guns used in the attack.