The man had initially denied the crime, but confessed during the trial. By the end of the hearing, however, he had denied the crime again.
The woman's body was found last summer under the deck of a house in Nybro, southern Sweden. The son admitted to burying the woman, but claimed that someone else had murdered her.
The verdict was initially scheduled for late March, however the discovery of the convicted killer's laptop meant a postponement to the case.
The computer was discovered with traces of blood, and a hard drive containing search history detailing scores of hits on websites pertaining to murder.
There were 67 pages viewed about penalties for murder, forensic investigations, homicide during psychosis, and choices of forensic institution.
The man was not found to suffer from any serious psychiatric disorder.
The court ordered the man pay 50,000 kronor ($7,785) in damages to his younger sister, as well as 25,000 kronor to the woman's widower.