I don’t know of any aalims in Washington DC…but until you find an imam who can provide you with further knowledge about this case…my advice is to treat the black magic with verses from the Quran. As this is the recommended Islamic treatment.
You can recite the three Quls, Ayatul Kursi, last 2 verses of Surah Baqra, and surah Fatiha. These are all beneficial in treating black magic. You can recite and blow on the person. You can also recite and blow on the food and water that the person drinks. And you can recite and blow throughout the house.
It is said that recitation of surah Baqara keep shaitan/jinn away from one’s house. I’ve included a helpful link below. Also, encourage the person to get medical treatment. It is possible that his illness is due to some pyschological problems for example schizophrenia, paranoia, etc.