A female security guard at a Rockland County library was fatally stabbed when she asked the suspect to turn down the music he was playing on his phone, according to a report.

Blanchard Glaudin, 25, has been charged with second-degree murder after being tackled by patrons at the Finkelstein Memorial Library in Spring Valley, The Journal News/lohud.com reported.

“He was walking just a few feet away,” village Police Chief Paul Modica said Wednesday about the “random” confrontation a day earlier.

“She was at the computer terminals and told him he had to turn it down. That was it,” he said, referring to Sandra Wilson, 52, who was pronounced dead at a local hospital.

Wilson, who had two grown sons and a grandchild, had worked in clerical jobs at the library before joining its security team, the news outlet reported.

Rockland DA Thomas Walsh II commended “the brave citizens, who reacted without fear for their safety, by subduing the suspect. We will ensure that justice is served in this horrible crime.”

Modica said Glaudin had previously lived in Florida, where “he had some run-ins,” but did not provide details about the suspect.

He also said he did not know if any library security guards were armed, adding that “a couple retired police officers work there.”

Modica said his thoughts go out to Wilson’s family and her co-workers.

“They were taking it pretty hard,” Modica said of the staff and patrons who witnessed the shocking crime. “It really was a horrific thing.”