Seeking a noun for 'one who knows things are bad but doesn't act' [duplicate]

I'm looking for another noun to describe someone who knows things are bad, but doesn't do anything to improve the situation because of fear of the consequences of acting.

Ostrich is the closest I can get but it doesn't fit with the six other labels I'm using; it introduces an unwanted comic element. Also, the ostrich pretends not to know: I'm trying to describe someone who knows perfectly well, but feels paralysed. Paralysis could work but it's not a noun used for a person; I can't use paralytic because that would have completely different connotations.

Cambridge Dictionary:

spineless adjective (disapproving) ​

A spineless person does not have much determination and is not willing to take risks:

He was, she concluded, a spineless individual.

Ditherer: Noun. Chiefly [British English] a state of indecision. Verb. To be nervously irresolute in acting or doing. (The Free Dictionary - online)

So, one might say, "He is a ditherer. He is unable to make the necessary decisions to save the company from an aggressive takeover by corporate raiders".

Might 'bystander' fit?

I don't fully understand the context; but a 'bystander' can be, for example, somebody who witnesses a crime or something immoral and doesn't do anything to improve the situation.

Not to be confused with 'innocent bystander', which implies that the person was distant or unable to act.

Good luck!

I think coward is the right noun.

"a person who lacks the courage to do or endure dangerous or unpleasant things."

Or perhaps they lack temerity. Temerity is:

"the quality of being confident and unafraid of danger or punishment especially in a way that seems rude or foolish."

If your target audience is adults in an informal setting, then the slightly profane would do nicely: "pussy", as in, "John knew the answer to question the professor was asking, but he's such a pussy that he remained silent, for fear of being thought a nerd by his classmates.

...or, an example more to the "knows things are bad but doesn't act" requirement: "The bank manager knew that all it would take was a quick press of the hidden button to notify the police the bank was being robbed, but he's such a pussy that he remained motionless, for fear of being beaten or shot by the robbers."