Lester Shubin, a government scientist who saw the potential of using Kevlar to strengthen bullet-resistant vests for the police, an advance that has saved the lives of more than 3,000 officers, died Nov. 20 at his home in Fairfax, Va. He was 84. The cause was a heart attack, his son, Harry, said. Working with the Army in the early 1970s, Mr. Shubin helped develop the first vests made of Kevlar, an extraordinarily strong fabric invented by the DuPont Company. At the time he was a program manager with the National Institute of Justice, an arm of the United States...