The girl was last seen waiting for the ice cream truck, pedaling slow circles on her bicycle in the street four lots down from her house in Mesa, Ariz.

Ninety seconds later, 11-year-old Mikelle Biggs was gone, the bike toppled over, wheels still spinning. The quarters Biggs had brought along to pay for the treat were scattered on the ground.

“She was running from somebody,” a police detective would surmise on ABC’s “20/20” in 2009. “It wasn’t somebody that she knew or wanted to be with.”

Mikelle’s disappearance on Jan. 2, 1999, launched a massive hunt — national news coverage, consultations with psychics, searches through abandoned mine shafts, possible suspects identified and then dropped. All the effort, however, produced no answers about what happened to the sixth-grade honor student who played clarinet and wanted to be a Disney animator when she grew up.

Nineteen years later and 1,700 miles away, a message on a one dollar bill has reignited interest in the case.

Police in Neenah, Wis., revealed this week that they received the bill, according to the Appleton Post Crescent, with a message scrawled in the margins: “My name is Mikel Biggs kidnapped From Mesa AZ I’m Alive.”

The note, with its misspelling of Mikelle’s name, has already raised questions of authenticity. But this week, law enforcement in Arizona confirmed they were investigating the bill. The question remains whether the message is tied to the disappearance — or if, like so many other once-promising leads, it will turn into another frustrating dead end.

“Someone out there clearly recalls the case, whether it be Mikelle or someone else,” Mesa police detective Steve Berry told ABC 15 on Tuesday. “So is that a clue one way or another? We just simply don’t know at this point.”

During the initial rush to locate the girl, police fielded more than 10,000 tips, the Arizona Republic reported. One call informed police that Mikelle was being held at a Motorola plant, but that proved to be a hoax. Another email pointed police to a house outside Phoenix — again, a hoax, just a 12-year-old kid on a computer.

Mikelle’s father, Darien, was considered a suspect, then later exonerated. A neighbor living two blocks away had a criminal record of child molestation, but no evidence tied him to Mikelle. The case went cold, with police receiving fewer leads as the years passed.

“We always follow up on [tips],” Berry, of the Mesa police, told the Arizona Republic. “We always hope that might be the one that breaks the case.”

The dollar bill was turned into police in Neenah, outside of Appleton, on March 14. “A man came to the front lobby and dropped it off,” Police Chief Kevin Wilkinson told ABC News. “He found it in a collection of money for Girl Scout Cookies.”

Two problems immediately jump out regarding the message. First, Mikelle’s name is misspelled in the note as “Mikel.” Secondly, according to police, the dollar bill was printed in 2009, 10 years after the her disappearance.

“The oddity in the note is that her first name is spelled wrong,” Wilkinson said this week. “That certainly seems odd, and it would sway you to believe that it might not be legitimate. But why would you pick that one, a case that’s nearly 20 years old? It’s somebody who knew something about that case.”

Neenah police investigator Adam Streubel told the Arizona Republic that even if the bill was somehow linked to Mikelle, there is no feasible way to trace the tender’s route to Wisconsin.

“There was a little spring of hope for a second, and then reality set in,” Streube told the paper. “There is nothing you can do with it, which is rather frustrating.”

The Mesa police are currently working with authorities in Wisconsin to pull possible clues from the bill, Berry told The Washington Post.

“Fingerprints would be very difficult on a dollar bill of that age,” Berry said. “Handwriting perhaps is something we can look at.”

Mikelle’s little sister, Kimber, told the Republic she was also suspicious of the message.

“I don’t believe she would have written it, as the circumstances of it don’t make much sense,” she told the paper. “There’s always that bit of hope, but I think right now we just want it to lead to someone who knows something.”

More from Morning Mix: