NEW YORK — It was dawn in the cellblocks of Dannemora, time for a round of bed checks on the convicted killers, rapists and other criminals held behind stark 19th-century walls. Guards went along the lattice of light-green bars in “A” Block, where well-behaved prisoners are held.

At first glance, it seemed David Sweat and Richard Matt were where they were supposed to be: asleep in their adjoining cells. But the lumps in their bunks were just sweatshirts. The convicted cop killer and the career criminal doing time for dismembering his boss had squeezed through holes neatly cut in the steel wall behind their beds, penetrated a brick wall and a steam pipe, and emerged from a manhole outside the Clinton Correctional Facility’s 40-foot wall.

“Have a nice day!” they smirked in a note left along the way.

It would be the last authorities would hear from them for three weeks, until officers found and killed Matt on Friday in woods near the Canadian border, about 30 miles from the prison, and captured Sweat nearby Sunday.

The June 6 escape spotlighted apparent security lapses in a prison where a complex escape plan may have been rehearsed for weeks and the breakout went undetected for as long as six hours.