OK - here is where I believe I read the clerk talked about the man in the Tom Thumb:
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http://www.immelman.us/news/missing-person-joshua-guimond/
Sidebar: Suspect Sketch in Wetterling/Guimond Investigation
Below is a police sketch Fox 9 KMSP-TV in the Twin Cities used in a February 2004 feature about a college student working at the Tom Thumb convenience store in St. Joseph, who rented the video “Naked Gun” to Jacob Wetterling minutes before his abduction on October 22, 1989.
According to the Fox 9 report, this man came to the Tom Thumb store two weeks to the day after the abduction and talked obsessively about Jacob, saying, “They’ll never find that boy” (note the depersonalization of the victim in that st<span class="searchterm2">atement).
The clerk thought this individual, described as a white male about 50 years of age (or about 70 in 2009) with receding gray hair, was behaving suspiciously. She reported him to the FBI and apparently the sketch was produced based on her eyewitness account.
This person closely matches the description of a suspicious person seen lurking around the Tom Thumb store and other area video rental places on the day of Jacob’s abduction.
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With regard to the name of clerk, as shergal has said above, I also think the clerk gave an account of what happened that night in a talk that was made either on the campus of St. John, printed in the St. John's newsletter, or in a Public Radio broadcast (I remember reading that account, as shergal has said.) Says above that there was a news item about the clerk's experience: Fox 9 KMSP-TV in the Twin Cities used in a February 2004 feature. Wonder if there is further info. in this feature.