On the afternoon of July 31, 1990, 60-year-old coin dealer Charles William Sparboe and his 47-year-old assistant, Catharine Newstrom, were found shot in the head at the Treasure State Silver & Gold shop in Billings, Montana. About $54,000 worth of coins and gold had been taken. Sparboe had told others he was uneasy about a new customer who said he was a farmer from nearby Laurel and wanted to invest proceeds from a farm sale; Sparboe’s son Jim recalled the man parking a silver Pontiac at a distance and noted the man’s unusually smooth hands for a farmer. Jim left the shop that day and returned to discover the two victims.

The Billings case was later tied to a series of similar robberies and killings of coin shop owners in several states. A composite led investigators to Charles Thurman Sinclair, alleged to have revisited shops to gain owners’ trust before returning near closing time to rob and kill. Sinclair was arrested in Kenny Lake, Alaska, on August 16, 1990; Montana charged him and sought extradition. Sinclair died of a heart attack in his Anchorage jail cell on October 30, 1990, leaving the Billings murders unresolved in court.

Did anyone who knew Sparboe, Newstrom, or their customers remember that suspicious man or the silver Pontiac in late July 1990?