When Kenneth P. Thompson was a young federal prosecutor in Brooklyn in the late 1990s, he was assigned to one of the biggest cases the office had ever handled, that of the police officers accused of beating and sodomizing Abner Louima, a Haitian immigrant.

The officers were white, Mr. Louima black, and the harrowing episode rekindled racial tensions and anger at the police in New York City in 1997.

So Mr. Thompson was taken aback when Loretta E. Lynch and another senior prosecutor in the case, which went to trial in 1999, told him he would be delivering the much anticipated opening statement. “That tells you a lot about Loretta,” Mr. Thompson, now the Brooklyn district attorney, said of Ms. Lynch, the United States attorney for the Eastern District of New York, who was nominated by President Obama on Saturday to be the nation’s next attorney general.

The Louima trial is perhaps the clearest gauge of Ms. Lynch, 55, as a prosecutor, associates say: a calm, under-the-radar lawyer who could also fight hard when it helped her cause. During that case, she was willing to work in the background when needed, and she relied on a keen sense of courtroom tactics rather than rhetoric. Though race was a bitter undercurrent of the entire case, she rarely focused on it — until the defense tried to. Then she and her team took the potentially explosive issue head on.