As the death penalty fell out of favor in the United States, the influence of the unit, already one of the smallest in the Justice Department, waned. About half a dozen trial lawyers worked there in the beginning of 2012, along with a lawyer conducting protocol reviews and three others on loan from different parts of the department.

Mr. Carwile had arrived just before the public learned of the Fast and Furious scandal, a botched operation in which agents at the Bureau of Alcohol, Tobacco, Firearms and Explosives let criminals move guns across the border into Mexico to try to build a bigger case. Many of the firearms were later found at crime scenes. Mr. Carwile incorrectly told superiors that the A.T.F. learned about guns moving illegally only after the fact, according to a subsequent inspector general investigation. He was moved from his post as head of the gangs unit to the much smaller capital punishment division.

Image Kevin Carwile arrived to run the Justice Department’s death penalty division in 2010.

He quickly gained a reputation as a mercurial manager with a hands-off style that bordered on neglect, according to current and former employees. He rarely responded to emails, four former employees said, and in meetings his questions revealed that he had not read their messages.

But after his first year, Mr. Carwile received the Excellence in Management award for the criminal division as the section’s lawyers prosecuted more cases.

In 2013, Jacabed Rodriguez-Coss, a prosecutor who had herself won one of the department’s highest awards, complained to human resources that Mr. Carwile expected her to involuntarily travel far more than her male counterparts.

Though she lived in Connecticut and had cases in Rhode Island and Vermont, he assigned her to one in California. She protested that her family needed her nearby. Her husband, an F.B.I. agent, was one of the first on the scene of the shooting at Sandy Hook Elementary School and was confronting the aftermath of having worked on the case.