Pacheco lived in the 1200 block of Luawai Street in Honolulu, Hawaii in 1966. She was engaged to marry Albert A. De Mattos, who lived in the 900 block of Koae Street in Honolulu. De Mattos was 73 years old in 1966 and, like Pacheco, is of Portuguese descent. Photographs and additional vital statistics for him are unavailable. He had been married twice before becoming engaged to Pacheco. Pacheco had only known him three weeks prior to their disappearances.

The couple visited De Mattos's son on December 9, 1966 and afterwards, between 8:00 and 9:00 a.m., they went for a drive together, saying they were going to the laundromat and would return soon. De Matto was apparently carrying between $700 and $800 in cash when they were last seen. Pacheco called her daughter at 2:00 p.m. and told her she and De Mattos were going for a drive. Neither one returned. A stew was found cooking in Pacheco's apartment after she vanished.

The police initially did not take De Mattos and Pacheco's disappearances seriously, thinking they had merely eloped without telling anyone and would return eventually. Investigators became concerned after months passed with no sign of either person or De Mattos's gray/blue 1957 Pontiac sedan with license plates numbered 5A-31514, which they had been riding in. The only possible sighting of them was in a Sears, Roebuck & Co. department store in Honolulu, where a clerk claimed to have served them a month after they vanished. This sighting has not been confirmed.

Both De Mattos and Pacheco's prescriptions have not been refilled or their bank accounts accessed since their disappearances. De Mattos had $6000 in a joint bank account he shared with his son, and was expecting more money from an apartment building he sold shortly before his disappearance. Pacheco is described as a dependable woman who always kept in close contact with her teenage daughter, but none of her family members ever heard from her again after she disappeared with De Mattos.

Pacheco and De Mattos's cases are no longer being investigated by law enforcement due to the passage of time since they vanished, but their families have never forgotten them. It is not known whether they left voluntarily together, or if other factors caused their disappearances. Their disappearances continue to puzzle people.