A law enforcement official says that in the Connecticut school shootings, the 20-year-old suspect killed his mother at their home and then drove his mother's car to the school where he went on the rampage.
Twenty small children and six teachers were massacred on Friday when the gunman walked into a quiet suburban Connecticut school armed with sophisticated handguns.
Connecticut State Police spokesman Lieutenant Paul Vance said 18 children were killed inside Sandy Hook Elementary School and that two more died of their wounds in hospital.
Six adults at the school were killed, including its principal, before the killer was shot -- either by his own hand or police.
There were very few non-fatal injuries reported, indicating that once targeted, there was rarely any chance of escape, and that the gunman was unusually accurate in his fire.
Vance said the majority of killings 'took place in one section of the school, in two rooms.' He was reported to be carrying at least two handguns.
Local media reported that the shooter began in the kindergarten section where he killed his teacher mother and her class, then moved on. The child victims were reported to be aged between five and ten.
Initial media reports quoted police sources identifying the shooter as 24-year-old Ryan Lanza. However, after initial confusion, police now believed the killer may be Lanza's brother Adam, 20.
Adam Lanza's mother, Nancy, was a teacher at the school, the law enforcement official said.
Meanwhile, in New Jersey, Adam Lanza's older brother, Ryan, 24, of Hoboken, New Jersey, was being questioned by police, said a second official. Earlier, a law enforcement official mistakenly transposed the brothers' first names.
The officials spoke on the condition of anonymity because they were not authorised to speak publicly about the developing investigation.
Ryan Lanza was extremely cooperative during questioning late Friday by law enforcement in New Jersey, said the second law enforcement official who was briefed on the investigation.
He is not believed to have any involvement and is not under arrest or in custody, but investigators were still searching his computers and phone records, said the second official.
Lanza told authorities that his brother was believed to have suffered from a personality disorder and be 'somewhat autistic' and lived with their mother in Connecticut, the official added.
The first official said Adam Lanza had died from a self-inflicted gunshot wound.
According to the second official, the suspect drove to Sandy Hook Elementary school in his mother's car.
Three guns were found at the scene - a Glock and a Sig Sauer, both pistols - and a .223-calibre rifle. The rifle was recovered from the back of a car at the school. The two pistols were recovered from inside the school.