The campus was shut down Monday afternoon due to the extensive graffiti, which included swastikas and threatening comments.
Investigators said Stephen Lazarus has admitted to the vandalism. He was booked at the East County Sheriff's Station and held on $50,000 bail.
The investigation determined the suspect acted alone and authorities believe he did not have the means to carry out any credible threat.
The graffiti has been painted over. Justin Elementary resumed its normal class schedule Tuesday.