Except for close contact with Dellen Millard on the final days of their lives.
I wonder who else they had close contact with?
We have no idea when DM and LB last saw each other, she could have met with many people in the days before going missing, so by that logic they should all be suspects.
WM may have been home at his house while DM was out for dinner, we have no idea who had a key to that house or whether the door was left open or who entered that house, if anyone, to kill him, if he did not kill himself.
We also have no idea who the third person was on a test drive, or if they met anyone else. We don't know if test drive ended and TB was followed by someone else. The accused have kept their right to remain silent, so we have no idea what really happened at this point or who may have been in close contact with him prior.