WASHINGTON — Days after a huge bomb killed 168 people in Oklahoma City in April 1995, Merrick B. Garland was on the ground even as bodies were still being recovered, examining the crime scene and preparing for an eventual prosecution.

“It’s pretty somber when you’re looking at a desk with a jacket on the chair and a bottle of Coke, and a foot and a half away there is no floor — it’s just open air,” said Donna A. Bucella, a former colleague who went with Mr. Garland to survey the devastation.

Now a federal appeals court judge and a potential Supreme Court nominee, Judge Garland was then the highest-ranking Justice Department official dispatched to Oklahoma City in the aftermath of the bombing. He spent the ensuing weeks helping to start the case, and later supervised the prosecutors from department headquarters.

For Judge Garland, the Oklahoma City bombing was the centerpiece of a constellation of federal criminal cases in which he played a role before President Bill Clinton appointed him to the Court of Appeals for the District of Columbia Circuit in 1997.