A ransom note dropped in the mailbox at the home of missing 9-year-old Charlotte Sena before dawn on Monday provided investigators an invaluable break in the case that ultimately led New York authorities to arrest a suspect and reunite the girl with her family after a frantic two-day search, state officials announced.

Fingerprints left behind on the note were instrumental in identifying suspect Craig Nelson Ross, Jr., 47, and tracking him to a residence where law enforcement arrested him Monday evening and immediately found Charlotte hidden in a cabinet, Gov. Kathy Hochul announced in a news conference.

The girl appeared "outwardly physically unharmed" and was taken to a hospital to be examined, the governor said.

Ross was still being questioned late Monday night and had yet to be charged, Hochul said, noting charges are "fully expected."

"Everyone in New York is breathing a collective sigh of relief right now," Hochul said on CNN's "AC360" Monday night.

Charlotte went missing on Saturday during a family camping trip at New York's Moreau Lake State Park, sparking an around-the-clock search involving hundreds of personnel from multiple agencies, including the FBI, state police said.

Hochul outlined the meticulous steps taken by investigators once the ransom note was discovered early Monday and described how cell phone data and other evidence aided in the case. Here's what we know.

The path to discovering Charlotte

At around 4:20 a.m. ET Monday, the suspect drove by the Sena family home and placed the ransom note in their mail box, according to Hochul. Despite the early hour, Charlotte's parent's were still at the campsite searching for their daughter.

When state police discovered the note, they were able to recover fingerprints from the document and began running them through law enforcement databases to see if they could find a match, the governor said.

A hit came at 2:30 p.m., identifying the fingerprint as Ross', the governor said. Ross' fingerprint had been entered into the database for a 1999 incident of driving while intoxicated, she said.

Investigators then determined Ross may have been living in a residence behind his mother's home. Two state and federal SWAT teams descended upon residence in helicopters, made entry and arrested Ross around 6:30 p.m., Hochul said. Charlotte was immediately found inside a cabinet.

"She knew she was being rescued," the governor said. "She knew she was in safe hands."

In addition to the fingerprints, investigators also analyzed cell phone pings around the park at the time of Charlotte's disappearance, Hochul told CNN Monday night. Additional insight came from park records, which contain information about visitors who paid an entrance fee or registered to camp overnight, she said.

All of these investigative measures culminated in Charlotte being returned to her family, Hochul said.

"They were able to bring her to safety. And not long after, she was in the arms of her parents at a hospital," the governor said.

'Every parent's worst nightmare'

Charlotte's parents were confronted with "every parent's worst nightmare" when their daughter took off on her bike Saturday and didn't return, Hochul said.

The girl was last seen around 6:15 p.m. Saturday in Moreau Lake State Park, a popular recreation site about 45 miles north of Albany. She had been riding her bike with friends around one of the park loops and wanted to do one more loop by herself, according to the governor.

But Charlotte's mother reported her missing around 6:45 p.m. when her daughter's bike was found abandoned in the loop and the 9-year-old was nowhere to be found, Lt. Colonel Richard Mazzone of the New York State Police said.

As time went on and the search for Charlotte expanded across several counties, authorities began to fear she had been abducted, Hochul said.

"As each hour went on, hope faded. Because we all know the stories," Hochul said.

State police described Charlotte in a news release as "a bright and adventurous girl who loves to be outside."

"Charlotte has a huge heart and wants to create a club at her school for kids who don't have friends. She always put others first," state police said, assuring the public they were working tirelessly to find her.

By Monday morning, the search encompassed 46 linear miles and drew about 400 search and rescue personnel from state, federal and local law enforcement agencies, as well as private groups and dozens of volunteer fire departments, state police said.

"It was an awesome sight to witness ... everyone doing their job," Hochul said Monday night, thanking those who worked to find the girl.

"There were a lot of parents out there among the ranks and everybody thinks, 'If it was my child, I would want everybody under the sun looking for them.' And that's what this team did," she said.