SACRAMENTO, Calif. (CN) — A federal grand jury on Thursday indicted a father and son on accusations they kidnapped U.S. Forest Service employees in California and held them hostage for almost a day. According to law enforcement, Joseph Henrichsen encountered two Forest Service employees who were conducting frog habitat studies in the Shasta-Trinity National Forest, near Gumboot Lake Campground, on July 16. Walking to the trailer, the Forest Service workers saw Phoenix. His father told him to clear space in the trailer for them to sit, an FBI agent wrote in an affidavit. He then used the employee’s phone to make several calls, leaving a voicemail for someone he knew, the agent wrote.