Peter Lanza was taken in for questioning, but there was no indication he would face any charges, one U.S. law enforcement official told CNN.
Ryan Lanza was taken into custody for general questioning Friday from a home in Hoboken, New Jersey, according to three law enforcement officials. They did not label him a suspect.
The more complicated story of Adam Lanza was still being assembled by authorities and media in the aftermath of the massacre.
Authorities on Saturday said they were examining the sequence of events that led Adam Lanza to dress in what a law enforcement source said was "black battle fatigues and a military vest," enter Sandy Hook Elementary and begin firing.
He was named by authorities as the invader who shot to death 20 children -- ages 6 and 7 -- and six adults, then killed himself.
Adam Lanza was found dead in a classroom, and police recovered three weapons from the scene: a semiautomatic .223-caliber rifle made by Bushmaster and two handguns made by Glock and Sig Sauer, a source with knowledge of the investigation said.
Adam Lanza had no known criminal record, a law enforcement official said.
A member of Lanza's family told investigators that he had a form of autism, according to a law enforcement official who spoke under condition of anonymity due to the sensitive nature of the investigation.
Acquaintances struggled with fathoming the deadly actions being attributed to someone they had known.
Alex Israel was in the same class at Newtown High School with Adam Lanza, who lived a few houses down from her.
"You could definitely tell he was a genius," Israel told CNN, adding she hadn't talked with him since middle school. "He was really quiet, he kept to himself."
His former bus driver, Marsha Moskowitz, told CNN affiliate WABC that he was "a nice kid, very polite" like his brother.
"It's a shock to even know (the family)," she said. "You can't understand what happened."
A former classmate told CNN affiliate WCBS that Adam Lanza "was just a kid" -- not a troublemaker, not antisocial, not suggesting in any way that he could erupt like this.
"I don't know who would do anything like this," the classmate said, before walking away distraught. "This is unspeakable."