"Will the left ignore this story or try to deify this monster?"

Why would they?

FTA
"while they were out, he took his mother's gun and ammunition from her bedroom."

So the mom was so negligent she left a gun and ammo where her upset teenager (who she must have known was upset) could easily access it. And she paid for it with her life. How many times will we have to read tragic stories like this before gun owners learn to lock up their guns?

You would think gun owners (especially with kids) would learn that guns are deadly weapons and not playthings and should always be locked up when not needed.

And it sounds like in that household the knives should have been locked up too.

I just watched how the left reacted to Clancy murdering her 3 kids and how the left reacted to Luigi Mangione assassinating a man in cold blood.

No you didn't. You just watched YOUR reaction

It's a mix reaction obviously.

Regarding Left-leaning sympathy

Surveys from organizations like CloudResearch found that only around 25% to 28% of self-identified liberals expressed "some" degree of sympathy or support for his actions. That's less than a third.

The folks who appear to support Luigi were from a mix of political backgrounds:

Healthcare System Critics
from both the left and right
Online "Fangirl" Factions and Admirers;
Both left and right
Conspiracy Theorists:
Left and right
Vigilante Sympathizers:
Both parties

As for the Clancy murders that one is extremely complicated and is not even over yet apparently as it was not resolved. And yes there was a clear political divide. But. I don't think they will retry it because I think that the issue of free will and mental illness is too complex to be resolved in any courthouse. As became obvious by the case ending in a mistrial.