I just saw the movie moments ago. I think that Newt had some sort of prior knowledge of Grindelwald through his relationship with Dumbledore and therefore recognised something about him. He may also have seen the deathly hallows pendant before Graves passed it to Creedence.

ON EDIT: I am re-answering because I just finished reading the screenplay. There is no mention that Newt saw or noticed the Deathly Hallows on Graves -- so that assumption of mine is wrong. Nor is there any mention that Newt had prior knowledge because of Dumbledore, but that doesn't mean that is incorrect -- just not written into the screenplay, making it a guess at best.

The newspapers were filled with stories about Grindelwald. He is renowned or feared as a great wizard. All the magical community has Grindelwald on their minds.

My new answer is that the sheer scope and skill of his magic is what gives Newt the idea that Graves is Grindelwald. That is why Newt uses the Revelio spell.

I read the screenplay with this question in mind. Thanks @steelersquirrel

The newspapers were filled with stories about Grindelwald. He is renowned or feared as a great wizard. All the magical community has Grindelwald on their minds.

I think the sheer scope and skill of his magic is what gives Newt the idea that Graves is Grindelwald. That is why Newt uses the Revelio spell.

I just saw the movie moments ago. I think that Newt had some sort of prior knowledge of Grindelwald through his relationship with Dumbledore and therefore recognised something about him. He may also have seen the deathly hallows pendant before Graves passed it to Creedence.

I just saw the movie moments ago. I think that Newt had some sort of prior knowledge of Grindelwald through his relationship with Dumbledore and therefore recognised something about him. He may also have seen the deathly hallows pendant before Graves passed it to Creedence.

ON EDIT: I am re-answering because I just finished reading the screenplay. There is no mention that Newt saw or noticed the Deathly Hallows on Graves -- so that assumption of mine is wrong. Nor is there any mention that Newt had prior knowledge because of Dumbledore, but that doesn't mean that is incorrect -- just not written into the screenplay, making it a guess at best.

The newspapers were filled with stories about Grindelwald. He is renowned or feared as a great wizard. All the magical community has Grindelwald on their minds.

My new answer is that the sheer scope and skill of his magic is what gives Newt the idea that Graves is Grindelwald. That is why Newt uses the Revelio spell.

I read the screenplay with this question in mind. Thanks @steelersquirrel