Their faces covered in black soot, three adults safely rescued after several days in an inactive West Virginia coal mine were mobbed by loved ones in a teary reunion, then they thanked the crews that got them out.

The three walked out of an ambulance at a fire hall in Whitesville to the screams of relatives for a brief reunion Wednesday night before being taken to a hospital.

Cody Beverly told news outlets the four-day experience inside Elk Run Coal's Rock House Powellton mine near Clear Creek "was terrible."

"I'm with my family now. I'm fine," he said.

Beverly later told NBC News "Anybody who was involved in searching for us, I just want to thank you with everything inside of me," he said. "This is the biggest lesson I've ever learned in my life. This is a life-changing experience for me."

"We appreciate every one of you guys," said Kayla Williams, who also was among those rescued.

Williams' father, Randall Williams, said she had gone into the mine in search of copper.

People in the region do "whatever they can do to make money if they ain't got a job," Randall Williams told CBS News .

Raleigh County Prosecutor Kristen Keller said Thursday the sheriff's office is conducting a criminal investigation into the latest incident. She said the two offices began discussing potential charges when the search began Sunday.

Raleigh County Sheriff Scott Van Meter said Thursday the criminal investigation will focus on why the adults were in the mine and find out "what happened." Van Meter hadn't seen Randall Williams' comments but said people trying to steal copper from West Virginia mines is "nothing new."

Late last month crews abandoned their search at another West Virginia mine for a missing man suspected of stealing copper. Two other men who were arrested indicated the third man had gone inside a mine, but the search was called off after a team encountered unsafe conditions.

And earlier this month two men were arrested on charges that they broke into another mine in Boone County. Investigators said they, too, were looking for copper.

"It is a disturbing trend with people entering abandoned mines to steal copper wiring," said Boone County Chief Deputy Chad Barker. "I can't stress how dangerous this idea is and it's only a matter of time before we get a less desirable ending."

Abandoned coal mines contain toxic levels of gas, collapsing roofs, flooding, and other dangers may exist.

"When operations cease and a mine is sealed, conditions can deteriorate very quickly," said Eugene White, director of the West Virginia Office of Miner's Health, Safety and Training.

The latest search effort had prompted Gov. Jim Justice to issue a plea for people to stay away from nonworking mines.

According to the mine safety office, coal has not been mined at the Rock House Powellton mine for two years. It is among about 120 mines on "approved inactive" status in the state, meaning they could be reactivated at some point, Department of Environmental Protection spokesman Jake Glance said in an email.

Inactive mines are not permanently sealed but operators are required to secure the portals to prevent entry, he said.

"So in order for people to get in the mines they have to trespass and then somehow vandalize the existing barricade to gain entry," he said.

Mines that stopped operating prior to August 1977 are considered to be abandoned. There is no requirement for operators to seal those mines, since in many cases the companies no longer exist. A state Abandoned Mine Lands program, funded by fees on coal production, pays for projects such as sealing abandoned mine portals.

The sheriff's office had identified those rescued Wednesday as Beverly, 21, of Dorothy; Kayla Williams, 25, of Artie; and Erica Treadway, 31, of Pax. They had been missing since Saturday. A fourth person, Eddie Williams, 43, of Artie, walked out of the mine Monday. An abandoned ATV the four were believed to be riding was found near the mine's entrance.

Williams' aunt, Sandra Scarbro of Clear Creek, told The Register-Herald of Beckley, "We got our Christmas miracle. All we really know is she's alive, and we're so thankful that she's out and that they're all out. We appreciate everybody in the community, the governor and rescuers, everything everybody has done."

Crews had used fans to move fresh air into the mine while pumps cleared some standing water inside the mine but the water levels remained too high and hampered search efforts.

"My shoes were soaked, and I couldn't get my feet warm," Treadway said as she was being placed on an ambulance stretcher.