Jose Bustos-Diaz and Octavio Ramos Lopez turned up missing Tuesday.
TDCJ Inspector General John Moriarty says so far there is no indication of collusion by any prison employees. He says officials are trying to "build a case against anyone that's helped them" from the outside.
Bustos-Diaz was serving 35 years for murder in Harris County.
Lopez was convicted in Hidalgo County, serving 20 years for aggravated kidnapping and 12 years for drug counts.