PARIS—The key defendant in the 2015 Paris attacks trial said Wednesday the coordinated killings were in retaliation for French airstrikes on the ISIS terrorist group, calling the deaths of 130 innocent people “nothing personal” as he acknowledged his role for the first time. Salah Abdeslam, who wore all black and declined to remove his mask as he spoke in a custom-built courtroom, has been silent throughout the investigation. Observers were waiting to see if he would offer any details during the trial. Nine ISIS gunmen and suicide bombers struck within minutes of one another at several Paris locations on Nov. 13, 2015, targeting fans at the national soccer stadium and cafe-goers and ending with a bloodbath in the Bataclan concert hall. It was the deadliest violence to strike France since World War II and among the worst terror attacks to hit the West, shaking the country’s sense of security and …