The boy was found near Sellersburg in Washington County, Indiana Saturday, CNN reported.
Police described the suitcase in which he was found as having a hard-shell with a bright, bold pattern, featuring a "Welcome to Las Vegas" sign.
An autopsy on the child didn't determine a definitive cause of death.
A toxicology report may provide more answers, but that could take three to six weeks.
Authorities said the top priority right now is determining the boy's identity.
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They believe he was about 5 years old and died within the last week.
He was a thin child, roughly 4 feet tall.
Police said they don't have any solid indication that he was from the area, so the search for clues is nationwide.
A national tip line has been set up.
Anyone with information that could help identify the boy is urged to call Detective Matt Busick with the Indiana State Police at 1-812-248-4374 or 1-800-872-6743.
