Zuzu Verk was last seen the night of October 11 in Alpine, Texas.
Classes have been canceled or polling has been moved from schools in various districts due to fears of violence during this tense election.
The siblings — who are originally from Michigan — walked free after officials interrogated them and searched their laptops, an official confirmed.
More than half of patients are between 15 and 19.
Government intern Chandra Levy disappeared in 2001 before being found murdered.