One key element is his use of deception. He presented himself as a normal, friendly person, which allowed him to get close to his victims. Another is his choice of victims, mainly young boys and men. Also, the fact that he buried many of his victims in his own home is quite significant. It shows his boldness and how he thought he could get away with his crimes.
Well, in the full story of John Wayne Gacy, his ability to blend in was a key element. He was like a wolf in sheep's clothing. He had a normal - looking exterior that masked his inner evil. His crimes were systematic. He had a routine when it came to finding, subduing, and murdering his victims. The psychological aspect is also important. What drove him to commit such atrocities? And finally, the way his case was investigated and how the evidence was gathered against him to convict him of his many crimes is a vital part of the story.