Laws are the source and in this case Maryland law. I am not a lawyer. Md has a wiretap / no audio recording of unaware parties.
https://law.justia.com/codes/maryland/2015/article-gcj/title-10/subtitle-4/section-10-402/
This is MD Cam law https://law.justia.com/codes/maryland/2010/criminal-law/title-3/subtitle-9/3-903/