San Bernardino County sheriff's officials said prosecutors would be making a decision on what charges to file within the next 48 hours.
Lee had reportedly planned to take Corwin on a hunting trip the same day she disappeared.
"We certainly believed in the beginning her disappearance was suspicious," San Bernardino County Sheriff John McMahon said.
Corwin had planned to search the park for areas to visit when her mother came into town to celebrate Corwin's 20th birthday, which was July 15. But when she did not return, her husband, Lance Cpl. Jonathan Corwin, reported her missing the following day.