First let me say that law enforcement in the USA is inept at best. Law enforcement officers or agents are only interested in furthering their careers. The amount of energy they put into a case depends on how good a write up they think they will get.
If your crime was something like underage porn, or WMD, then you can bet that they will spend the energy because the arresting officer will get a lot of accolades. If it is something less, then they will likely not bother because their goal is to further their career, not to uphold the law.
Yes, they can obtain the files even if you deleted them. If you placed them on social media (facebook, instagram) then you are pretty stupid. Facebook and Instagram keeps copies of everything you upload.