GRINNELL, Iowa (AP) — State investigators are investigating the death of a man in the custody of Grinnell police.

Iowa Division of Criminal Investigation special agent Mike Motsinger told The Des Moines Register that 54-year-old Ronald Shook died Monday after being in Grinnell police custody for less than a day. Motsinger says an autopsy Tuesday revealed no external signs of trauma. More results are expected within six weeks.

Why Shook was taken into custody near railroad tracks that run through Grinnell is unclear.

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Information from: The Des Moines Register, http://www.desmoinesregister.com