Wisconsin police investigating letter threatening Easter church attacks

The author of the letter claims to be fugitive Joseph Jakubowski.

The Waukesha Sheriff's office is currently determining the authenticity of the letter, which threatened violence against a number of unspecific churches on Easter Sunday.

"At this time, while the investigation continues, we are unable to substantiate the threat nor its author," a statement from the sheriff's office said on Thursday.

The letter suggested the threats would be in the Sussex area of the county, some 25 miles northwest of Milwaukee.

The hunt was schedule for Saturday, and a statement put out by Walker and First Lady Tonette Walker said they were "sad to miss one of our favorite events."

The Associated Press and ABC News' Michael Edison Hayden, Julia Jacobo, and Adrienne Bankert contributed to this report.