Patrick C. Fischer, a computer scientist whose theoretical work helped make Internet searches possible, but who was most widely known as an early target of the so-called Unabomber, died on Aug. 26 in Montgomery County, Md. He was 75.

The cause was stomach cancer, his family said.

Mr. Fischer was a professor of computer science at Vanderbilt University in Nashville, Tenn., when a pipe bomb concealed in a package addressed to him exploded in his office on May 5, 1982, while he was lecturing in Puerto Rico. The package was opened by his secretary, Janet Smith, who suffered lacerations and burns on her chest, arms and hands. She returned to work after three weeks in the hospital.

Investigators told Mr. Fischer that he was apparently the fifth person targeted by the mail bomber, who was identified in 1996 after his arrest as Theodore Kaczynski, a Harvard-trained mathematician.

The attack came to represent a kind of unsolved equation for Mr. Fischer. He later described scouring his memory for any possible links he might have had with Mr. Kaczynski in the late 1950s and early '60s, when both were graduate students in Cambridge, Mass. But while they knew many of the same people, he could not remember ever having met Mr. Kaczynski.

"My original research was pure math," he told The Washington Post. "Maybe I was regarded as a turncoat by this guy. I went from pure math to theoretical computer science."

Mr. Kaczynski, who is serving a life sentence for mail bombings that killed three people and injured 28 between 1978 and 1995, singled out professors, scientists and business leaders.

Mr. Fischer grew up in Ann Arbor, Mich., and earned his Ph.D. from the Massachusetts Institute of Technology. After teaching at Harvard, Cornell and Penn State University, Mr. Fischer was chairman of the computer science department at Vanderbilt in 1980. He retired in 1998.

Mr. Fischer was among an early group of mathematicians working in the field of database theory. His study of the mathematics of query languages was crucial in the development of systems now commonly employed by Google, Amazon and every other website with a search box. But while the commercial application of his work helped give birth to a generation of billionaires, Mr. Fischer never regretted remaining a scholar. "He was an academic," said Dirk Van Gucht, a professor of computer science at Indiana University and former student of Mr. Fischer. "And he was a wonderful teacher."

First Published: September 3, 2011, 4:00 a.m.