More than 900 students were absent from three Orland-area schools after authorities say a man posted messages on Twitter, threatening to shoot students and put pipe bombs inside campuses.

News outlets reported that on Thursday there were 379 absences at Orange's Liberty Middle School, 357 at Orlando's Boone High School and 174 absences at Orlando's Edgewater High School. It is unclear how many students were missing from Orlando's Colonial High School, the fourth school named in the threats.

The FBI said Wednesday they were looking into the threats made against the schools, but didn't think they are credible.

Authorities are searching for the man who they say posted the threats: a 23-year-old transient who has lived in Florida, California, Virginia and Maryland.