Like thousands of mentally ill people in New York, Mr. Simon was repeatedly left to fend for himself on the streets, cycling through jails and hospitals for years without access to steady housing or remotely adequate psychiatric care. On one occasion in 2017, he apparently told a psychiatrist that he feared he would at some point push a woman off the subway tracks. The warning did not stop him from being released yet again. Some four years later, on Jan. 15, he shoved Michelle Alyssa Go, a 40-year-old Asian-American woman, in front of a southbound R train, killing her instantly....