(NewsNation) — In his 34 years in law enforcement, New York State Police Col. Richard Allen had never seen a ransom note be left by a child abductor.

But it was the one allegedly left in a mailbox early Monday morning that would lead police to a suspect in the abduction of 9-year-old Charlotte Sena, who was found alive later that night after a two-day search in upstate New York.

“Once we got this ransom note, it was the first real solid piece of evidence we had in this case,” Allen said Tuesday on “CUOMO.”

Craig Nelson Ross Jr., 47, was charged with first-degree kidnapping in the case, the Saratoga County Sheriff’s Office said Tuesday.

Charlotte went missing over the weekend while riding her bike early Saturday evening at Moreau Lake State Park, a heavily wooded area some 35 miles north of Albany.

She was found alive and safe Monday.

Investigators were able to identify a fingerprint from a ransom note allegedly left by the suspect.

The ransom note was left inside the mailbox of the Sena family home around 4 a.m. Monday, Gov. Kathy Hochul said. A fingerprint on the ransom note matched Ross, who was in a database from a 1999 DUI case.

Allen did not disclose exact details of the ransom note, but generally described it as “very basic.”

“Not much direction to it,” Allen said.

Police discovered the note after a vehicle pulled up to the house in the early morning hours of Monday, stopped briefly and then drove off. A trooper posted at the home found it suspicious enough to investigate the mailbox, Allen said.

“When he found that note, I mean, immediately for us it was game, on a lot of work that we had to get done,” Allen said. “This note was really the key piece of evidence that … allowed us to be able to bring Charlotte home.”