An MD80 was level at FL340 heading north, about to descend. The controller did not detect a converging eastbound B737 and, therefore, cleared the MD80 to descend to FL300. When the MD80 started its descent, a Short Term Conflict Alert was triggered. In the attempt to rectify the error, the controller instructed the MD80 to stop the descent. Under stress, he issued a confusing instruction for the B737 to turn. The pilot did not respond. At this point, both aircraft received a coordinate RA: The MD80 received a Climb RA that he followed correctly while advising the controller. The B737 pilot received a Descend RA, which was also complied with. As a result of the coordinated Climb and Descend RAs, the two aircraft passed each other with a vertical separation of 1400 feet and a horizontal separation of 0.6 nautical miles. A simulation undertaken later showed that the vertical separation would have been only 100 feet without these maneuvers. 3. Who or what is responsible for the occurrence of the incident?