Jack Kilborn is a pseudonym for bestselling author JA Konrath, creator of the Lt. Jacqueline "Jack" Daniels series.
When Joe writes a dark thriller or a horror novel, he publishes it under the pen name "Jack Kilborn" in order to differentiate it from his other books. Kilborn tends to be less humorous and more violent, with a higher scare-factor.
Jack and Joe have also collaborated on many books, to make it even more confusing for fans. They both apologize for this.
You can visit Jack at www.JackKilborn.com.