Data retrieved from the suspect's smartphone shows he has looked up several people.
The list includes residents at addresses which were targeted in shootings that the police and the prosecution believe Mangs is responsible for.
Mangs today admitted he had kept tabs on around one hundred different individuals.
"I wanted to get information about journalists, politicians and criminals," he said in court in the southern town of Malmö.
Assistant prosecutor Håkan Larsson asked why he collected the information but claimed repeatedly in court that he remembers very few details of his research.
"It was of interest of me at the time," replied Mangs. "then it stopped being of interest."