When the controller said "radar contact," the conflicting head-on VFR target would only have been 1/2 inch away on the scope. As a controller myself, it is difficult to imagine that a target within that proximity would have been missed. I can understand occasionally neglecting to scan about a target due to one's attention being focused elsewhere on a task, but in this case full attention had to be focused directly on the target of the Wings West aircraft. When a controller says "radar contact," the controller is looking directly at that target symbol. And then when the controller verifies the altitude with the pilot, the controller must once again focus directly at the target. Attention couldn't have been diverted, as the Wings West target was the airplane receiving the full attention of the controller just prior to the collision.
The other item of compelling interest is that this was no ordinary day for the controller working that aircraft. This was a developmental controller who was taking a check ride for sector certification. This is not a time when one slacks off, as one's career progression is on the line. How well one performs during this checkride means everything. And not only was the developmental there, but so was his instructor, right behind him, with full unobstructed view of the scope. And the data position, which is immediately to the right of the scope, was manned by a third experienced controller. And overseeing the certification check ride was a supervisor. None of them noticed any VFR traffic in front of the Wings West aircraft. The two that were ultimately charged with the responsibility of viewing the scope (the developmental and his instructor) testified that the target of the VFR aircraft was NOT displayed.
It was frustrating for me to read the transcript of the NTSB investigation. Many questions were asked, but I could find no mention whatsoever of the software radar data processing method of "selective rejection" discussed, or even brought up. Could this have played a part in this midair collision?
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