This remarkable story of <400 words is both stunningly simple & packed with layers of meaning & deep allusions which outwit the most knowledgeable audiences.
1/100 sheep lost
1/10 coins lost
Then 2 sons, both lost, though 1 is found again, & the fate of the other depends on the audience's response.
The sheep is lost by going away
The coin is lost staying at home
This story tells of two sons, 1 lost by going away & the other lost at home.
So here, Older Bro doesn't want to recognize Younger Bro, as Scribes don't want to recognize Sinners.
Ditto Lazarus (16:21).
Where in Scripture, other than Luke 15:20, does a man run, fall on someone's neck and then kiss them?
He ran, fell on the neck of younger brother returning from herding in distant land, + kissed him (Gen 33:4).
Toll Collectors + Sinners may have missed the allusion. But what about Scribes?
Parallels with Jacob & Esau story run deep. Jacob goes with nothing to far land + returns with lots.
Prodigal goes with lots + returns with nothing.
In Luke, Older Bro has inherited whole farm + is angry at risk of loss when Little Bro comes back prepared to work for his food.
The Joseph story also has embraces though the kissing and falling on the neck, though only as separate events (Gen 45:15; 46:29).
So that’s 3 big OT stories: Jacob-Esau, Jacob-Laban, and Jacob-Joseph which Jesus has worked into this parable.
The Older Bro thinks he's being treated as a slave when he is a son.
Meanwhile, echoes of Judah should have reminded Bible expert Scribes that Judah asked his younger brother to be treated like a slave (Gen 44:33).
Servant: ‘Your father has killed the fattened calf’; Older Bro to Dad: ‘You killed the fattened calf FOR HIM’.
So the one who wanted his father dead is not Younger Bro, who wanted the inheritance, but Older Bro, who wanted Dad out of the way.
The only possible answer: his imagination. Why does he imagine Younger Bro with prostitutes? That's where he like to be.