Air Traffic Control Developmental
Human-Machine Interface; Situational Awareness; Confusion
ATC Issue All Types; Conflict NMAC
Air Traffic Control Provided Assistance; Flight Crew Returned To Clearance
ATC Equipment / Nav Facility / Buildings
Aircraft X was eastbound at 7000 ft; Aircraft Y was westbound at 16000 ft the targets merged but I didn't call traffic being separated by 9000 ft. Aircraft X asked if we had any traffic because he had a near mid-air with traffic within 300ft. I issued the traffic at 16000 that merged ranged in the display as far as I could and still nothing. About 30 seconds later a primary target (Aircraft Z) appeared 3 miles behind Aircraft X. The primary target was not displayed or hidden from sight. Make the targets a different color than the data blocks. Maybe if it was hidden under the data blocks it would show up a different color.
ZFW Controller reported an aircraft under his control reporting a NMAC. The Controller had traffic 9;000 feet above this aircraft and did not see any other traffic. Controller zoomed radar scope in and saw nothing. Seconds later the Controller observed a primary target 3 miles south of the reporting aircraft.