Of course, too early to tell what is the motive here, but one thing did strike me about the phone call from a distressed woman that this couple seem to have known. The Teppes seem to be a couple that would go out of their way to help someone in a bad situation, for example, an abusive relationship. We've seen this before in a few cases, where the anger of the rejected male is meted out to the helpers of the abused woman, as without their influence, he perceives that she will be back under his control.
This couple would both be in their social circle and therefore would probably know the keypad code. Just speculation.