TUCSON, Ariz. — The investigation into the disappearance of Nancy Guthrie encountered another obstacle this week as Mexican authorities postponed a volunteer search prompted by an anonymous tip claiming her remains were buried near the U.S. border.

The 84-year-old mother of NBC "Today" host Savannah Guthrie was abducted from her home in the Catalina Foothills area near Tucson in the early morning hours of Feb. 1. Blood found at the residence belonged to Guthrie, authorities have said. Door camera footage released by investigators showed a masked individual outside her home.

Volunteer group Buscando Corazones had planned a third search along the Mexican-Arizona border on June 16 following a tip that Guthrie's "grave" was located near a stream and under a tree in an area known as Mariposa in Nogales, Sonora. The search was indefinitely delayed because Mexican authorities were unavailable to accompany the volunteers.

The group, which assists in locating missing persons in Mexico, requires the presence of local authorities for protection during searches, though they are not formally involved in the official investigation. Ramona Guadalupe Ayala Ortiz, who leads Buscando Corazones, said volunteers had previously checked the area identified in the tip but found no supporting evidence.

Pima County Sheriff's Office, the lead agency in the case, issued a statement acknowledging awareness of........

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