Olsson said the 41-year-old son was found by a relative who then alerted authorities.
The woman denied any wrongdoing, Olsson said, adding that the son had been admitted to hospital for treatment for “the physical injuries he sustained when he was found.”
“We can’t talk about what kind of injuries,” Olsson said.
Swedish newspaper Expressen said the man was found on Sunday by a relative who learned the elderly woman had been admitted to hospital. The relative went to the apartment, found the main door unlocked and entered it.
The relative, who was not identified, told the daily that there was “urine, dirt and dust” everywhere and “it smelled of rot”.
She heard a noise coming from the kitchen and found the man sitting on blankets and pillows. According to the relative’s report in the diary, he had no teeth, had sores on his legs, and his speech was blurred.
“He spoke very fast and a little inconsistently, but he was not afraid of me,” said the parent quoted by Expressen.
The daily said the man’s apparent captivity began 28 years ago, which would have made 13 at the time.
Olsson said investigators will interview the mother, son and witnesses.