Some time that night someone entered the Moore home. Locking up your home wasn't a habit for residents of Villisca in 1912; it may not be a habit still. So the killer didn't need to force entry.

The killer held in his hands an axe he'd picked up as he rounded the side of the Moore home.

He took out Josiah Moore and his wife Sarah first. The killer used the blunt edge of the ax initially, but upon returning to the master bedroom he must have been concerned that Josiah Moore was not yet dead, and he went to work with the blade.

Then the killer attended to the children, Herman, Catherine, Boyd, and Paul.

The Stillinger girls were murdered while sleeping in a downstairs bedroom. It was in the attack on the sisters that the killer's real motive may have been revealed. That, or a psychopathic killer decided to take additional advantage of a situation not previously anticipated. Found near the bed where the Stillinger girls died was a slab of bacon taken from the Moores' icebox. One of the girls had been positioned in a sexual manner, though it was never reported that either girl was raped. Investigators have long suspected that the slab of bacon was used as a masturbatory aid by the killer.

Then, alone in the house with his own madness and eight dead, brutalized bodies, the killer apparently went to every window, drawing curtains, and spreading aprons. He also covered a mirror inside the home. He may have stayed in the Moore home for hours after the massacre.

Villisca: Living with a Mystery does an excellent job of detailing the events spiralling out from that horrific night. The Rundles trace how later suspicions and accusations derailed the political career of one man and drove another man, already troubled, even further into madness. And they finally make a compelling case for the Moores having been victims of a particularly terrifying and mobile serial killer.

For there were at least 20 other murders that happened in the midwest in the same time period that had strikingly similar elements. All of these murders have been tentatively attributed to a man named Henry Lee Moore. From the Stevens Point Gazette (WI), an issue published May 14, 1913:

Henry Lee Moore went to the penitentiary at Jefferson City after being found guilty of the murder of his mother and grandmother, Mrs. Mary Wilson and Mrs. George Moore, at Columbia Mo., in December, 1912. Moore made many damaging admissions and contradictory statements.

He said he had made a study of famous murders, including the Dr. Crippen case in England. The ax murders ascribed to Moore [...] are:

H. C. Wayne, wife and child; Mrs. A.J. Burnham and two children; Colorado Springs, Colo., September, 1911. William B. Dawson. wife and daughter, Monmouth, III. October, 1911.
William Showman, wife and three children, Ellsworth. Kan.. October, 1911.
Rollin Hudson and wife, Paolo, Kan., June, 1911.
J. B. Moore, four children and two girl guests. Villisca, Ia. June, 1912.
Mrs. Wilson and Mrs. Moore at Columbia...