Investigators hunting Nancy Guthrie’s kidnappers have one glaring clue that’s been staring at them from the beginning — a Bitcoin wallet sent by ransom note writers to Guthrie’s family.

Crypto experts say the ransom note and the wallet suggest that the kidnappers were “farkakta” amateurs, but detectives are also reportedly wondering if they made a massive, $152 blunder at the start of the case.

A ransom email — which mentions details about Guthrie’s home and an Apple watch that hadn’t been disclosed to the public — demanded $4 million in crypto for her return.

Instead, the FBI deposited $152 in Bitcoin into the wallet — hoping the potential kidnappers would transfer the money out, allowing cyber experts to track them down.

But it’s still sitting there to this day.

“[The suspects] would want to get those $4 million off chain as fast as they can,” explained Ari Redbord, global head of policy at TRM Labs, a data firm that helps law enforcement solve crypto-based crimes.

“They are typically using mainstream exchanges like Coinbase or Kraken that have that user information. … Law enforcement can then subpoena them for that information,” he told The Post.

But instead, the FBI opted to deposit a much smaller sum in the account.

The strategy — called “tickling the wire — might have worked, especially because Guthrie’s bumbling kidnappers probably wouldn’t use more sophisticated tools to cover their tracks.

“An actual, sophisticated operation wouldn’t have gotten involved in a kidnapping conspiracy turned homicide. That alone says it’s rookie s–t,” said attorney Todd Spodek, who specializes in cyber crime and represents alleged $16 million fraudster Ronald Spektor. 

A suspect was filmed in a cobbled-together Walmart mask/glove ensemble with a gun awkwardly holstered on his pants, trying and failing to disable Guthrie’s doorbell camera on the day she vanished.

Even if that bumbling thug had been working with a computer-savvy mastermind: “It sounds like some f–king, and I don’t know any other word than the yiddish, but some farkakte plan,” Spodek said.

Yet both Spodek and Redbord agree that choosing to not send the $4 million was also a valid option for law enforcement.

Meanwhile, the task force is still trying to track the ransom notes authors by following the chain of proxy servers the sender, or senders, used to protect their identities.

Authorities also detained and released several persons of interest, canvassed Tucson-area gun stores, and analyzed potential DNA evidence — all to no avail as the investigation enters its fifth month.