Investigators have found “some very good evidence” to explain what drove a 20-year-old gunman to slaughter 20 children and six adults at an elementary school in the small Connecticut town of Newtown, the site of one of the worst mass shootings in U.S. history, an official said on Saturday.

The attacker, identified by law enforcement sources as Adam Lanza, opened fire on Friday morning at Sandy Hook Elementary School, which teaches children aged five to 10. He is suspected of killing 26 people at the school before turning the gun on himself, as well as killing one other person at another nearby site.

“Our investigators at the crime scene, the school, and secondarily, at the secondary crime scene that we discussed where the female was located deceased did produce some very good evidence in this investigation that our investigators will be able to use in hopefully painting the complete picture as to how and more importantly why this occurred,” Connecticut State Police Lt. Paul Vance told a news conference.

Vance did not describe the evidence but did say the shooter forced his way into the school, as opposed to being let in.

“We have established the point of entry,” Vance said. “I can tell you it was — it’s believed he was not voluntarily let into the school at all, that he forced his way into the school but that’s as far as we can go on that.”

Crime-scene investigators worked through the night and moved the bodies to the state medical examiner’s office for autopsies, the police said. Victims’ names had yet to be released.

The adult woman found at the secondary crime scene was related to the shooter, a police news release said, and many media outlets have reported it was the shooter’s mother, Nancy Lanza.

On Saturday, authorities released the identities of the victims of the Sandy Hook Elementary School shooting:

  • Charlotte Bacon, 6
  • Daniel Barden, 7
  • Rachel Davino, 29
  • Olivia Engel, 6
  • Josephine Gay, 7
  • Ana M Marquez-Greene, 6
  • Dylan Hockley, 6
  • Dawn Hocksprung, 47
  • Madeline Hsu, 6
  • Catherine Hubbard, 6,
  • Chase Kowalski, 7
  • Jesse Lewis, 6
  • James Mattioli, 6
  • Grace McDonnell, 7
  • Ann Marie Murphy, 52
  • Emilie Parker, 6
  • Jack Pinto, 6
  • Noah Pozner, 6
  • Caroline Previdi, 6
  • Jessica Rekos, 6
  • Avielle Richman, 6
  • Lauren Russeau, 30
  • Mary Sherlach, 56
  • Victoria Soto, 27
  • Benjamin Wheeler, 6
  • Allison Wyatt, 6

According to the Chief Medical Examiner, all of the young victims were in first grade.

- With files from The Associated Press