After the World Trade Center was bombed in 1993, the Port Authority of New York and New Jersey made Douglas G. Karpiloff the director of security and life safety for the center. He installed an array of protective systems, including huge concrete planters around the towers, a strict set of building passes and an identification and tracking system for vehicles entering the basement. He was also called in to consult about security in Denver before Timothy McVeigh's trial for the Oklahoma City bombing and on how to protect the White House and other federal buildings. Last year, his industry trade group named him security director of the year.

"He was always trying to think out of the box," said Alan Reiss, the former director of the Port Authority's World Trade Department. "Doug set up all kinds of procedures that became the new norm for signature office buildings."

As he increased security, Mr. Karpiloff, 53, was concerned that the tenants he was trying to protect still be treated as people. That meant getting security guards to say good morning and putting out candy near the guard desks at Halloween. "Even if you were turned away, he wanted it to be a positive experience," Mr. Reiss said. "He came to me with all of these ideas, like, `I'm going to spend $2,000 on candy.' All of these little things made a dramatic difference."

After Silverstein Properties took over operation of the towers in July, Mr. Karpiloff had remained for a few months as a member of the transition team.

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