Cops have kept many of the grisly details sealed, but they're convinced that 15-year-old Joshua Young killed his younger sibling, 14-year-old Trey Zwicker.
The youngster was found beaten in a ditch outsider of a high school in May.
And now a grand jury in Louisville KY, has decided that he should be prosecuted as an adult, despite the fact that he was charged as an adult.
Zwicker's father Terry, who suggested to cops that they investigate Young, told WLKY that he welcomed the news but it was still difficult.
He said: "A lot of sad days, a lot of bad days. I'm sure there are more still coming, but now, it's anger. I have a lot of anger."
He added that he wants the harshest punishment for Young, and it's possible the 15-year-old could be eligible for the death penalty, if the Commonwealth decides to pursue it.