i suspect Laundrie brought NOTHING to the table in this relationship, a leech.
Maybe she broke up with him and he realized he would have to work/get a job/grow up and he got angry.
In most cases the parents protect their kid, look at Scott Peterson’s parents!
The poor woman was likely pregnant. Killing pregnant girlfriends has become just another form of abortion in some minds. If you thoroughly devalue the life of your own baby, it is not a leap to devalue the life of the baby's mother. Selfishness is too good a name for it, but that emotion is at the root of it.