The man says he did it for "fun" and the love of science:

The 31-year-old tells the paper that he was able to buy radioactive waste from foreign companies and picked apart the components in a smoke detector (apparently older smoke detector contain nuclear material). He believes he spent between $5,000 and $6,000 on the project in total.

It was only later when the young man contacted Sweden's nuclear power agency that he realized his project was illegal. Police came to his apartment and confiscated the material. The young man was arrested but later released.

The story reminded me of this old, beautiful thing: "Golf Manor is the kind of place where nothing unusual is supposed to happen..."