A former Air Force intelligence analyst said his guilt over participating in lethal drone strikes in Afghanistan led him to leak government secrets about the drone program to a reporter.

Daniel Hale of Nashville, Tennessee, is scheduled to be sentenced Tuesday in U.S. District Court in Alexandria after pleading guilty to violating the Espionage Act by leaking top secret documents.

In court papers filed Thursday, Hale’s lawyers asked that he receive a 12- to 18-month sentence, which would be well below sentencing guidelines.

In an 11-page handwritten letter from the Alexandria jail where he’s being held, Hale outlines what led him break the law, describing his regret and horror as he saw gruesome videos of Afghans killed in part because his work helped track them down.

Read more: AP