People talk about qualified immunity like it means a police officer is above the law. That's not true at all. When qualified immunity is working correctly, all it does is shift the liability from the individual to a higher authority (the department/city/state/etc).
In this case, it doesn't apply because theft isn't part of an officer's regular duties. You can't sue an officer for taking your laptop and putting it in evidence. You can sue an officer for taking your laptop home.