What are some other reasons Hitler persecuted the Sinti and Roma Gypsies?

I'm working on a project for my class and I need to know some other reasons for why Hitler persecuted not just the Sinti and Roma, but other gypsies as well besides the fact he thought they were a threat to the biology of the Aryan race and the fact that they were nomadic,foreign to the region, and I think the gypsies didn't assimulate with culture and society. If you have any information on this please let me know and thanks for your help, appreciate it.