When it comes to DIY suppressors, there's making your own from hardware scrap, making them from various oil and fuel filters, ordering them from an overseas vendor (Ali, Wish, etc) with the risk of customs, and now there's 3d printing.

You can print a fully workable 9mm suppressor on nearly any 3d printer in 8-10 hours or less with no post finishing necessary. No, common street criminals may not use them yet, but I don't think this shooter is a common street criminal, or a professional either.