Strange story that begins with the discovery of a statue then jumps to someone poisoning milk bottles and opening fire in a stadium. If you know it that is all you need. I composed an essay about its themes one night in my head but never wrote it down. Just something I need to do and the book is gone.
This matches up with "The Beast that Shouted Love at the Heart of the World" by Harlan Ellison.
The story includes many seemingly unrelated threads told in omniscient narration, ultimately connecting them with offhand mentions and details. The threads can be categorized as: events on Earth, events in an alien community known as the Concord, and descriptions of non-physical concepts.
A man, William Sterog, goes on a killing spree. He poisons two hundred people with an insecticide stolen from a pest control man, kills a hundred people on a jet flight by means of a time bomb planted in his mother's suitcase, and shoots 44 people on the stadium with machine gun, before he is arrested.
In presumably the far future, an expedition from Earth discovers a new planet with a 37-foot-tall (11 m) statue on it. The statue has an alien but beatific face. The figure is wearing a toga and grasping a strange object. The narration notes that the statue's expression is the very same that Sterog had when the judge sentenced him to death at his final court hearing.
The narration then goes on to describe a concept known as "Crosswhen" which is described as possibilities, outcomes, distance, and time all "beyond human thought."
Next, a violent and insane seven-headed dragon is captured and "drained" using a technique invented by an alien man named Semph. The dragon is described as being "crosswhen" to another subject referred to as "the maniac." The narration leaves it ambiguous to whether or not the maniac and the dragon are two distinct beings or perhaps even two distinct consciousness of the same mind. Semph talks with his rival, Linah, about the nature of the "draining." Semph argues that draining has possible consequence to others elsewhere while Linah, arguing on behalf of a community known as the Concord, argues that it is a necessary risk to ensure their own survival, even at the expense of others. The dragon is drained and the remnant, left behind following the draining, is a man. Semph then reveals that he has sent the drained aspects ("dangerous essences") elsewhere, not contained in a tank as planned. He alludes to these elements as part of an unelaborated "field." A panicked Linah demands to know where the aspects have been sent to....
Found with a DuckDuckGo search for
science fiction story dragon "poisoning milk" stadium