Story highlights Peter Lanza has claimed Adam Lanza's body, a family spokesman says

The spokesman says the body was claimed Thursday

Police say Lanza, 20, killed his mother and then opened fire in a Connecticut elementary school

He killed 20 children and six staff members at the school before killing himself, police say

The father of Sandy Hook Elementary School shooter Adam Lanza claimed his body last week, a family spokesman said.

Peter Lanza claimed the body Thursday, spokesman Errol Cockfield said. He declined to specify where the body would be buried.

On December 14, Adam Lanza , 20, took guns belonging to his mother, Nancy , and shot her as she slept in her bed. Then he went to the school in Newtown, Connecticut, where he gunned down 20 children and six staff members before killing himself.

It was one of the worst mass shootings in U.S. history.

Peter Lanza was questioned by authorities after the shooting, as was the gunman's 24-year-old brother, Ryan.

Authorities have offered few details about Adam Lanza. He had no known criminal record, authorities have said.

Photos: Funerals: Community says goodbye Photos: Funerals: Community says goodbye Newtown funerals: Community says goodbye – Mourners wipe tears away as they file out of the Church of Jesus Christ of Latter-day Saints after the funeral of Emilie Parker in Ogden, Utah, on Saturday, December 22. Hide Caption 1 of 30 Photos: Funerals: Community says goodbye Newtown funerals: Community says goodbye – The casket of Rachel Marie D'Avino is carried into the Church of the Nativity in Bethlehem, Connecticut on Friday, December 21. Hide Caption 2 of 30 Photos: Funerals: Community says goodbye Newtown funerals: Community says goodbye – Parents attend the funeral of Dylan Hockley, 6, a victim of the Sandy Hook Elementary School shooting, on December 21 in Newtown, Connecticut. Hide Caption 3 of 30 Photos: Funerals: Community says goodbye Newtown funerals: Community says goodbye – A view from outside the funeral service for 6-year-old Dylan Hockley at Walnut Hill Community Church on December 21. Hide Caption 4 of 30 Photos: Funerals: Community says goodbye Newtown funerals: Community says goodbye – Family members depart the Trinity Episcopal Church in Newtown, Connecticut, following a funeral for Benjamin Wheeler, 6, on December 20. Hide Caption 5 of 30 Photos: Funerals: Community says goodbye Newtown funerals: Community says goodbye – Mourners, including Boy Scout and Tiger Scout members, depart the funeral on December 20, 2012. Wheeler was a member of Tiger Scout Den 6. Hide Caption 6 of 30 Photos: Funerals: Community says goodbye Newtown funerals: Community says goodbye – Boy scouts salute as a funeral procession for Benjamin Wheeler enters the Trinity Episcopal Church on December 20, in Newtown, Connecticut. Hide Caption 7 of 30 Photos: Funerals: Community says goodbye Newtown funerals: Community says goodbye – Firefighters salute as the casket of Daniel Barden, 7, a victim of the shooting at Sandy Hook Elementary School, is removed from St. Rose of Lima Church on Wednesday, December 19, 2012, in Newtown, Connecticut. Hide Caption 8 of 30 Photos: Funerals: Community says goodbye Newtown funerals: Community says goodbye – Police escort the hearse bearing the casket of Daniel Barden from St. Rose of Lima Church on December 19. Hide Caption 9 of 30 Photos: Funerals: Community says goodbye Newtown funerals: Community says goodbye – Mourners enter St. Rose of Lima Church for the funeral of Charlotte Bacon, 6, on December 19, in Newtown. Hide Caption 10 of 30 Photos: Funerals: Community says goodbye Newtown funerals: Community says goodbye – A police officer directs traffic as mourners enter the church for Charlotte Bacon's funeral on December 19. Hide Caption 11 of 30 Photos: Funerals: Community says goodbye Newtown funerals: Community says goodbye – A procession arrives for the funeral of Victoria Soto, 27, at Lordship Community Church in Stratford, Connecticut, on December 19. Soto was a first-grade teacher being hailed as a hero for protecting the children in her class during last week's school massacre in Newtown. Hide Caption 12 of 30 Photos: Funerals: Community says goodbye Newtown funerals: Community says goodbye – A woman carries a program with Soto's photo after attending a funeral for the slain teacher in Stratford on December 19. Hide Caption 13 of 30 Photos: Funerals: Community says goodbye Newtown funerals: Community says goodbye – Bagpipers play at funeral services for Soto on December 19 in Stratford. Hide Caption 14 of 30 Photos: Funerals: Community says goodbye Newtown funerals: Community says goodbye – Richard and Krista Rekos leave after a funeral service for their 6-year-old daughter, Jessica, at Saint Rose of Lima Church on Tuesday, December 18, in Newtown. Jessica was one of 20 children killed in last week's school shooting. Hide Caption 15 of 30 Photos: Funerals: Community says goodbye Newtown funerals: Community says goodbye – Family and friends depart Jessica's funeral on December 18 in Newtown. Hide Caption 16 of 30 Photos: Funerals: Community says goodbye Newtown funerals: Community says goodbye – A child stands next to a makeshift memorial for Jessica Rekos following her funeral on December 18. Hide Caption 17 of 30 Photos: Funerals: Community says goodbye Newtown funerals: Community says goodbye – Pallbearers carry out James Mattioli's casket at St. Rose of Lima Roman Catholic Church after a funeral Mass on December 18 in Newtown. James, 6, was one of the 26 victims in the shooting at Sandy Hook Elementary School in Newtown. Hide Caption 18 of 30 Photos: Funerals: Community says goodbye Newtown funerals: Community says goodbye – Mourners console each other after the funeral for James Mattioli on December 18. Hide Caption 19 of 30 Photos: Funerals: Community says goodbye Newtown funerals: Community says goodbye – People arrive for the funeral of Jessica Rekos, 6, at St. Rose of Lima Roman Catholic Church in Newtown on December 18. Hide Caption 20 of 30 Photos: Funerals: Community says goodbye Newtown funerals: Community says goodbye – Jessica Rekos' casket arrives at St. Rose of Lima Roman Catholic Church as mourners gather December 18. Hide Caption 21 of 30 Photos: Funerals: Community says goodbye Newtown funerals: Community says goodbye – Mourners console each other after attending the funeral for Jack Pinto, 6, on December 17. Hide Caption 22 of 30 Photos: Funerals: Community says goodbye Newtown funerals: Community says goodbye – Mourners grieve the death of Jack Pinto, 6, on December 17. Hide Caption 23 of 30 Photos: Funerals: Community says goodbye Newtown funerals: Community says goodbye – A mother and two children attend the funeral for Jack Pinto on December 17. Children are among those crowding the funeral for the 6-year-old boy. Hide Caption 24 of 30 Photos: Funerals: Community says goodbye Newtown funerals: Community says goodbye – A man comforts a young mourner at Honan Funeral Home while attending the funeral for Jack Pinto, 6, on December 17. Hide Caption 25 of 30 Photos: Funerals: Community says goodbye Newtown funerals: Community says goodbye – Boys enter Honan Funeral Home before Jack Pinto's funeral on December 17 in Newtown. Hide Caption 26 of 30 Photos: Funerals: Community says goodbye Newtown funerals: Community says goodbye – Veronika Pozner, mother of Noah Pozner, arrives for her son's funeral on Monday, December 17, at the Abraham L. Green and Son Funeral Home in Fairfield, Connecticut. Monday is the first day of funerals for the 20 children and seven adults who were killed by 20-year-old Adam Lanza on December 14. Hide Caption 27 of 30 Photos: Funerals: Community says goodbye Newtown funerals: Community says goodbye – Three women embrace as they arrive for the funeral services for Noah Pozner on December 17. Hide Caption 28 of 30 Photos: Funerals: Community says goodbye Newtown funerals: Community says goodbye – Mourners arrive at Noah Pozner's service in Fairfield on December 17. Hide Caption 29 of 30 Photos: Funerals: Community says goodbye Newtown funerals: Community says goodbye – Mourners leave Noah Pozner's service on December 17 in Fairfield. Hide Caption 30 of 30

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A relative told investigators that the gunman had a form of autism, according to a law enforcement official, who spoke under condition of anonymity because of the sensitive nature of the investigation. CNN has not been able to confirm independently whether he was diagnosed with autism or Asperger's syndrome, a higher-functioning form of autism.

Geneticists are now studying Adam Lanza's DNA , a spokeswoman for the University of Connecticut Health Center said last week.

The geneticists were asked to join the investigation by the state medical examiner's office, spokeswoman Carolyn Pennington told CNN. She said that there is no specific genetic marker the team is looking for, and that lab results and a complete analysis of the DNA "are not expected for several weeks ... probably the end of January."

While experts agree that there are genetic components to many mental illnesses, there are hundreds, perhaps thousands, of genes involved. Most believe that no single gene or mutation alone could foretell violent acts like those committed by Adam Lanza.

After the school massacre, Peter Lanza released a statement saying that his family is "grieving along with all those who have been affected by this enormous tragedy."

"Our hearts go out to the families and friends who lost loved ones and to all those who were injured," the father said. "We are in a state of disbelief and trying to find whatever answers we can. We, too, are asking why."