Father-of-two shot dead daughters before turning gun on himself, police said
David Kaser, 56, fatally shot Clarissa Kaser, 19, and Crystal 'Grey' Kaser, 14
Investigators said David was on phone with his wife when he murdered his kids
Sand Springs, Oklahoma police were asked by his wife to do a welfare check
Police said they know the motive but 'won't be sharing it with the public'
When investigators arrived on scene, they knocked on door and got no response
Investigators found dead bodies of David and his two young daughters
Incident took place less than two weeks after triple murder-suicide in same town