Police opened an investigation Monday after eight books — most of them about Islam and the Quran — were reported as defaced with “graffiti and racist language” at Evanston Public Library.

Police were notified at 5:41 p.m. that the books, one of which was by author Glenn Beck, were defaced “with derogatory remarks” at the library at 1703 Orrington Ave., said Evanston Police Cmdr. Joe Dugan.

A statement on the library’s website said the books were marked with “graffiti and racist language and imagery.”

The Glenn Beck book was last checked out in June and the others have not been checked out since 2014 and 2015, Dugan said. An evidence technician was called to the scene to process the books.

“Since the time frame is so big it is going to be hard to investigate and get some leads if we cannot narrow it down,” he said in a statement. “We are currently working on a time frame of occurrence being June until Nov. 21.”

The library’s statement noted that librarians discovered the damage while preparing for a program about the Quran with Northwestern University’s Middle East and North African Studies program.

“The discovery of graffiti in books about Islam is troubling,” the statement said. “Free speech is one thing; defacing sacred texts and books about religion is quite another. Those who are caught defacing library materials will be prosecuted to the full extent of the law.”

Lorena Neal, a librarian at Evanston library, said in a Facebook post that the books were marked with “swastikas and racial slurs.” She added that the incident would be reported to the Southern Poverty Law Center.

“The Library provides a welcoming place to come together and discuss ideas and consider different points of view,” the library’s statement said. “The Evanston Public Library has a proven track record of fostering dialogue. Our partnership with Northwestern’s Middle East and North African Studies (MENA) program is an excellent example of bringing informative programs to our public library. One effective way to combat fear, hate and ignorance is to provide access to information, informed discourse, debate, and opportunities to listen to others.”