A US dollar bill found more than 2250km away from where an Arizona girl disappeared in 1999 is giving some investigators hope that a break in the decades-old case is possible.

Mikelle Diane Biggs, 11, was playing outside her home in Mesa, Arizona while waiting for an ice cream truck on January 2, 1999, when she vanished after being separated from her younger sister, Kimber, for about 90 seconds.

The girl’s bike had been thrown on the street and two quarters she previously clutched for her favourite ice cream treat were found nearby, but Mikelle had simply vanished.

Her disappearance set off a dramatic response, with a helicopter searching above Mesa within an hour and eventually leading to the police department’s most intense investigation ever, with more than 800 pieces of evidence collected and more than 10,000 tips received, according to the Arizona Republic.

The latest of those tips came in the form of a dollar bill from 2009 reported to police last week in Neenah, Wisconsin, where someone spotted a potentially useful clue in the search for Biggs, some 2338km away from where she disappeared 19 years earlier.

“My name is Mikel [sic] Biggs kidnapped From Mesa AZ I’m Alive,” a message written along its edges reads.

The girl’s name is misspelled, but appears to be written by a child, the Arizona Republic reports.

Neenah police investigator Adam Streubel questioned if the bill was genuine and noted that the girl’s first name is misspelled. The message could simply be a sick joke in a case that many investigators in the department, if not all, don’t remember vividly, he said.

“None of us were really aware of the kidnapping,” Streubel told the newspaper. “We had to do some research.”

But even if the message on the bill is authentic, there’s no way to track down who wrote it, Streubel said.

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

Still, police in Mesa plan to investigate the bill further after being alerted to it Monday, according to a police spokesman.

“We don’t get a lot of tips anymore, but we occasionally do,” Mesa detective Steve Berry told the newspaper. “We always follow up on it. We always hope that might be the one that breaks the case.”

Biggs, according to the National Missing and Unidentified Persons System, would be 30 years old today.

This article originally appeared on the New York Post and has been republished with permission.