The last question screamed by a mom whose own son was hammering her to death was Why?

17-year-old Tyler Hadley bludgeoned his parents Blake and Mary-Jo Hadley to death with a hammer last Saturday, then threw a Facebook party just hours later.

According to an unidentified friend to whom Hadley recounted the murders, he first took away his parents' cell phones to prevent them from calling for help.

Tyle went on to beat his mother first, as she screamed one final question Why?!, then proceeded to bludgeon his father whom he locked eyes with after he walked into the room.

Apparently, Hadley had not realized that cleanup would take as long as three hours, according to the friend.

Reports say Hadley claimed to be possessed by the devil and had taken three ecstasy pills before the murders, as he couldn't do it sober.

The teen is charged with the murder of Blake and Mary-Jo Hadley  and is being held without bond.