How did 2 killers escape from a maximum security prison?

(CNN)Convicted killers Richard Matt and David Sweat pulled off the kind of prison break that would normally be fodder for movies -- except theirs might be even more astonishing.

Armed with a complex plot and power tools, the pair did what no one else has been able to do in the 170-year history of New York state's most populated prison -- escape from its maximum security walls.

Now, as authorities look for the men in three countries, many are left scratching their heads.

Here's what we know and don't know about their scheme:

The tools
What we know: Matt and Sweat, who lived in adjacent cells, apparently used power tools to cut through a concrete-and-steel wall at the Clinton Correctional Facility in Dannemora, New York, authorities said.

What we don't know: How in the world they got those power tools -- and how guards didn't hear them being used.

New York Gov. Andrew Cuomo said the prison, built in 1845, undergoes regular maintenance, so it's possible the tools came from workers who are often in the facility.

The company who employs the maintenance workers is cooperating with the investigation, New York State Police Maj. Charles Guess said.

The escape
What we know: After cutting through the steel walls of their cells, the two followed a catwalk "down an elaborate maze of pipes into tunnels and exited a series of tunnels at the manhole cover," the governor said.

What we don't know: How Matt and Sweat could have known the layout of the dark, complex labyrinth in the bowels of the prison well enough to make their way out.

The help
What we know: The investigation is so fresh that nothing has been publicly discounted -- including whether the men had help in their getaway.

What we don't know: Who that help may have come from. Did a maintenance worker leave behind power tools? If so, was it intentional or accidental? Did a guard help them out? Or did someone from the outside actually carve their way in to reach the back ends of their cells?

The freedom
What we know: The two men left only one message during their escape: A yellow note on a pipe that read, "Have a nice day!"

For Matt, this isn't his first time escaping prison. In 1986, he escaped from an Erie County jail, the New York governor's office said.

Upon his capture, Matt was sent to a maximum security prison in Elmira, New York in 1986 on charges of escape and forgery. He was released from the Elmira Correctional Facility in May 1990.

What we don't know: What the two men will do next.

"Because they're stone-cold killers, you would expect them to stop at nothing to get out of the prison and to maintain their freedom once they are out," CNN law enforcement analyst Tom Fuentes said.

"That means they could have invaded one of the local homes in that small down, killed the people, stole their car, and driven halfway across the United States by the time (authorities) even know they were gone. So the police are going to have to check for the well being of every resident in the town."