A Separate Peace

Gene ultimately caused Phineas’ death because he was the only one in the timeline of events who deliberately harmed Phineas. He wanted Phineas to be injured because he felt that Phineas did not want him to do well academically. He was also much happier without Phineas around because in a way, Gene took Phineas’ place. Gene obviously had many motives to cause Phineas' death, but he also had many ways he was responsible for his …

…telling Brinker how wrong he was. When Brinker suggested that they do something about preventing Finny from pitying himself, Gene made it clear that Brinker didn’t have his approval to do so. Gene challenged Brinker to calling the meeting by telling him how not to act towards Finny. If he had just let Brinker do as he pleased, Brinker would have never called the meeting, and Finny would have never fallen down the stairs.