Mangs was accused of three murders and 12 attempted murders, mostly of people with immigrant backgrounds, in Malmö between 2003 and 2010.
During the case he denied most of the charges against him, but had confessed to vandalism for having fired a shot through a shop window.
Mangs was found guilty of killing Trez West Persson who was sitting in her car at the time of the shooting. West Persson's mum, Jeanette Persson West, told news agency TT it was a relief that Mangs was found guilty, but that the punishment is less important.
"Of course he should be punished, that's the consequences of his action. But that isn't important to me. I'll never get Trez back, no matter what. Never ever. We'll have to live with this for the rest of our lives", she said.