Jim Frederick, a former foreign correspondent and editor whose 2010 book about an atrocity committed by American soldiers in Iraq was praised for its thorough reporting and acuity in parsing the psychological erosion of men in war, died on July 31 in Oakland, Calif. He was 42.

The cause was cardiac arrhythmia and arrest, said his wife, Charlotte Greensit.

Mr. Frederick spent most of his career at Time Inc. as a reporter and editor for Money and Time magazines. At Time, he was the Tokyo bureau chief, a senior editor based in London, managing editor of Time.com and managing editor of Time International before leaving the company in 2013.

His book “Black Hearts: One Platoon’s Descent Into Madness in Iraq’s Triangle of Death” explores a grievous crime committed by four American soldiers: the rape and murder of a 14-year-old Iraqi girl and the killing of her family in their small house in the village of Yusufiya, south and west of Baghdad, in March 2006.

Without blinking and without excusing, Mr. Frederick documented the intense and withering experience of a group of men who were poorly commanded, overwhelmed with stress and witness to myriad bloody calamities, including the deaths of comrades. One of the book’s most noted strengths was in demonstrating the state of mind of men who have seemingly been stripped of all sense of their humanity.