Police in general don’t need to show warrants to arrest people. In high profile situations it may be done to minimize political blowback, but clearly that is not a primary concern in this situation (except toward individual officers, which is why they are masking).
In many situations, they just need a documentable/articulable (to a judge, later) reasonable belief that a crime was occurring in their presence, or in other situations that a specific crime had occurred and there was a reasonable belief that person had committed that crime.
Resisting arrest, and impeding official business of a police officer are usually arrest-able offenses almost anywhere.
Details vary by jurisdiction and crime, but ‘you need a warrant to arrest someone’ is an edge case, not the common case. In those cases, it’s also often an indictment or bench warrant.
In many situations, they just need a documentable/articulable (to a judge, later) reasonable belief that a crime was occurring in their presence, or in other situations that a specific crime had occurred and there was a reasonable belief that person had committed that crime.
Resisting arrest, and impeding official business of a police officer are usually arrest-able offenses almost anywhere.
Details vary by jurisdiction and crime, but ‘you need a warrant to arrest someone’ is an edge case, not the common case. In those cases, it’s also often an indictment or bench warrant.