On the 40th anniversary of one of its darkest days, the University of Texas took possession of a box of documents related to the infamous massacre at the school's landmark tower. The university's Center for American History accepted the documents Tuesday from a bookstore chain pertaining to what was then the nation's worst mass shooting.

On Aug. 1, 1966, Charles Whitman went to the 28th floor observation deck and began shooting at people below. He killed 16 people and wounded nearly three dozen before police killed him about 90 minutes after the siege began.

The documents, originals and photocopies, were discovered in a box by a relative of Allen Hamilton, who was the school's security chief at the time. The relative recently brought the documents to an Austin bookstore, Half Price Books, and offered to sell them.

"He said he'd been cleaning out stuff," said Christian Kurtz, who inspected the materials when they were brought to the store. "He said he didn't want them to fall into the wrong hands. He told us what they were so we wouldn't be surprised when we saw them."

Once they determined the items to be authentic, officials at the Dallas-based bookstore chain, who declined to identify the seller and the purchase price, decided to buy the materials and then give them to the school, which already had an extensive file on the case.

"We can't forget our history," Don Carleton, the Center for American History's director, said Tuesday. "No matter how tragic an event, it's still part of our history."

Carleton said it would take about a month for researchers to go through the new material, which includes original reports submitted by officers at the scene. There also are some original vehicle information documents signed by Whitman when he was a student in 1965.

On one of two manila folders, with Whitman's name typewritten, is a handwritten notation, "Deceased," and the Aug. 1, 1966 date.

"It was exciting but made us nervous at the same time," said Kurtz, 37, who said reading the material was unsettling. "I grew up in Texas. I knew the framework of the story."

Carleton said it was doubtful Hamilton violated any laws when he kept the paperwork because there were no laws back then regarding document possession.

"In this business, we have papers and records that come from the most unusual places you could think of, mainly from people's attics and things like that," Carleton said. "Our business is to preserve this material and make it available."

Whitman, 25, was a Texas student and native of Lake Worth, Fla. He opened fire just before noon. A 17th death was attributed to him in 2001 when a Fort Worth man died of injuries he suffered when he was shot that day.

Authorities later determined Whitman also killed his wife and mother in the hours before he went to the tower.

In notes he left with their bodies, he said he wanted to spare them the embarrassment of what he planned to do. He was having marital, financial and academic difficulties, was upset with the breakup of his parents and particularly angry with his father.

"It's important that the record be as complete as possible, so we are grateful," Carleton said as he accepted the box of materials. "As an historian, where there are no records, there is no history."