Is there an idiom or concise phrase for seeing someone in mortal danger and doing nothing about it? [duplicate]

I like

"Fiddle While Rome Burns"

but it usually doesn't refer to doing nothing while individual people are in serious trouble.

I want something along the lines of

"Fiddle While Jim Is Having A Heart Attack Right In Front Of You"

The bystander effect

The landmark case of the killing of Kitty Genovese is a monumental example of the bystander effect when in 1964, more than 30 people may have witnessed her violent death and did nothing to help or even call the police until it was too late. This event ignited social psychological studies of the bystander effect or bystander apathy.

Or as Edmund Burke put it, "The only thing necessary for the triumph of evil is for good men to do nothing."

The bystander effect refers to the inertia or inaction to respond in a serious situation that results from the belief that someone else will step in and do it.

A phrase you could use might involve playing the bystander or standing idly by, the latter more often applying to a situation involving a more people or a movement.

"It was clear Jim was having a heart attack, but Bob absolved himself, saying he was just a bystander, not a doctor."

"Bob acted like a bystander, doing nothing as he watched Jim suffer a heart attack."