U.S. President Barack Obama is traveling to Newtown, Connecticut, Sunday to join in the mourning of the 20 young children and six adults shot dead in a gunman's rampage.

White House officials say Mr. Obama will meet with the families of those who lost loved ones at Sandy Hook Elementary School on Friday and thank first responders. The president also plans to speak at a nighttime vigil in the small affluent town about 120 kilometers northeast of New York.

Connecticut state police say the list of those killed includes the names of 12 girls and eight boys – all of them in the same grade and aged six or seven years old. The adult victims were all female and included the school's principal Dawn Hochsprung, who reportedly tried to stop the shooter, and 27-year-old teacher Victoria Soto, who is credited with saving some of her students by putting herself between them and the attacker.

Connecticut's chief medical examiner said all of the victims were killed at close range by multiple gunshots from an assault rifle. Earlier reports also placed two semi-automatic handguns near the shooter's body. Officials say the gunman died at the scene of a self-inflicted gunshot wound.

Medical examinations of the shooter – identified as 20-year-old Adam Lanza – are expected to take place Sunday, along with an examination of his mother reported to have been killed by her son at their home.

U.S. authorities have yet to identify a motive for the shooting, and so far, they say there was no note, diaries or letters left behind by Lanza. However, unidentified officials say there is some evidence that could lead to understanding a motive. Lanza is reported to have been quiet and socially awkward, but also very bright.

According to law enforcement officials, Lanza's mother legally owned the weapons allegedly used by her son in the massacre.

Friday's attack was the second worst school shooting in U.S. history. In 2007, a gunman killed 32 people at Virginia Tech University in Blacksburg, Virginia. Prior to that, the most notorious U.S. school shooting was the 1999 rampage at Columbine High School in Littleton, Colorado, where two teenagers killed 13 students and staff before killing themselves.