A trove of new documents and 911 calls give insight into Shane Tamura's mental health before he shot and killed four people in a Manhattan skyscraper.

The 27-year-old Nevada man left a note at the scene voicing anger that his mental illness may be linked to his having played football, officials familiar with the investigation told NBC News.

New York City Mayor Eric Adams reveals gunman Shane Tamura acquired part of his rifle from an associate on 'The Story.'