(CNN) -- Police have arrested a couple and charged them with kidnapping in the apparent abduction of two Amish girls in upstate New York this week, authorities said late Friday.
Stephen M. Howells II, 39, and his girlfriend Nicole F. Vaisey, 25, are being held without bond, according to the St. Lawrence County Sheriff's Office. Federal charges are also a possibility.
On Wednesday, an Amber Alert was issued after 6-year-old Delila Miller and her 12-year-old sister, Fannie, disappeared from a vegetable stand near their family farm in Oswegatchie, located about 50 miles from the Canadian border.
A witness told police the girls were tending to a customer who drove up in a white 4-door sedan and then disappeared when the vehicle pulled away, according to the Amber Alert.
The Amber Alert was canceled Thursday night after Delila and Fannie were apparently abandoned along a road in Richville, about 40 miles away.
"The children walked up to a home, knocked on the door of a stranger," St. Lawrence County District Attorney Mary Rain told CNN affiliate WWNY. "The stranger brought them home to their house and police were waiting."
She said the girls were "a little wet and cold," but otherwise healthy.
The investigation moved quickly on Friday, as "good police work" and tips from the girls led authorities to the suspects, said St. Lawrence County Sheriff Kevin Wells.
"We have two strong young girls," Wells said. "The reason we're able to make an arrest tonight is because of just how strong they are and things they're able to remember."
Two cars -- one white, one red -- were towed from the scene by authorities, affiliate WSYR reported. The house where Howells and Vaisey live is being processed for evidence, according to Wells.
CNN's Joe Sutton contributed to this report.