Three teenagers in Pennsylvania have anonymously apologized for spray-painting a swastika made of shaving cream at a local library last Friday, slipping a letter containing $50 into a book depository.

The act of vandalism occurred in the parking lot of the Exeter Community Library in Berks County, according to a Facebook post from the library's director.

Police and firefighters were called to the scene to remove the Nazi symbol, but the case remained unsolved throughout the weekend.

On Monday morning, according to WJAC-TV in Johnstown, library staff found an envelope containing an apology and cash.

In their letter, the vandals described themselves as "three stupid teenagers apologizing for our heinous acts," adding that they did not mean to offend anyone. The teens further claimed that they all have religious roots and "did not intentionally mean this as any form of hate speech or dislikeness toward any culture."

The incident comes amid a disturbing wave of anti-Semitic bomb threats around the country and the vandalism of hundreds of headstones at Philadelphia's Mount Carmel Jewish Cemetery late last month. Investigators continue to search for suspects in the Mount Carmel case.

The reward for information leading to a conviction and arrest now stands at $74,000.