Gib bitte mal den deutschen Satz und den Kontext (was ist z.B. 'this'). Kann sein, dass Du "everyone" statt "anyone" einsetzen musst und dass nach dem "isn't" noch was hinkommen muss - usw.

Anyone who watches this happen and pretends it isn't happening is guilty.
(of what?)

Or:
Anyone watching this (happen) and pretending it isn't happening is guilty.

I don't think the "happen" needs to be repeated as the "watch(ing") implies it.

Yes, I agree with dude about dropping the 'happen' though I'd stick with pretends rather than pretending, because the latter seems to imply that the pretence is limited to the duration of the watching:

Anyone who watches this and pretends it isn't happening is guilty.

(I'd still like to know some more context: guilty of what? Maybe guilty isn't the right word. What's the preceding sentence?)

complicit vielleicht eher als guilty? Oder must accept some of the blame?

"Anyone's guilty who watches this happen and pretends it isn't"

Diesen Satz findet man genau so im Internet, offenbar aus dem Film "Mississippi burning. Da gibt es dann nur noch die Frage zu beantworten: ist er richtig?

Ich meine nein, es sollte heißen "... it doesn't".

#5 seems right to me to think along the lines of complicity (becoming an accomplice) without a clear original sentence we will all just come up with more or less appropriate guesses.

edit # 6 is just truncated from pretends it isn't happening see #4

Möglich, aber das steht nun mal nicht da. Und der Satz existiert unabhängig von melones Frage. Wollt ihr den Film neu vertonen lassen mit den vorgeschlagenen Varianten und complicit statt guilty?

Ist der folgende Satz korrekt: "Anyone's guilty who watches this happen and pretends it isn't"---Oder gehört da noch irgendwo die -ing Form dran? (OP)

No, it's not correct. And yes, an "-ing" is necessary.

The simplest solution, I would say, which hasn't been suggested so far, is as follows:

"Anyone's guilty who watches this happening and pretends it isn't."

Having written that, and before clicking on "Absenden," I googled "who watches this happening" and, lo and behold:

FSM Board: Who said that MEN didn't came from the APE??
www.filmscoremonthly.com/.../posts.cfm?...‎Diese Seite übersetzen
04.02.2001 - 20 Beiträge
Anyone is guilty who watches this happening and pretends it isn't. He was guilty all right, just as the fanatics who pulled the trigger. Maybe we ...

Someone somewhere along the line seems to have erm dropped something.

;-)

Viking you googled the info re film - this was not in the OP my post was written before I saw your note,