One came home that night.

The other, who is now being called a hero, did not.

The men started their day in the same place: the first-floor offices that house the Musculoskeletal Biomechanics Laboratory, where they studied how the human frame responds to muscle fatigue and neurological disorders.

One of the husbands, Kevin Granata, 46, a professor of biomechanics engaged in developing engineering mechanisms to help children cope with cerebral palsy, chatted a bit with the other researchers there before going upstairs to his third-floor office to meet with a graduate student he was advising.

Kevin Granata's brother-in-law, Michael Diersing, a 54-year-old laboratory administrator, stayed behind on the first floor, said researcher Gregory Slota, 30, who was there as well. Diersing, Slota and one other student were alone in the office when they heard a "pop, pop, pop" that at first sounded like construction noise. It was the beginning of what would eventually become the worst shooting rampage in U.S. history and an event that would forever alter this family. When it was over, 33 people lay dead.

When the shooting started, four students rushed to safety in the office, including one who had been shot by the attacker, Slota said. The group looked out into the hallway and saw that the exit had been chained shut. Members of the group, now numbering seven, debated what to do, and decided to lock themselves inside. They bound the wound of the young man who had been shot, using a T-shirt as a tourniquet. Barricaded inside, they stayed there until the attacker killed himself and police told them that the danger had passed.

Lois Diersing and Linda Granata heard of the attacks from news reports and called to make sure their husbands were OK. Slota was able to tell Lois that Michael was fine and that he would call her soon. Linda began calling for Kevin, and others began calling him, too, but his phone rang unanswered. Once the sisters, 48, learned that Lois' husband was safe, they frantically tried to find Linda's husband.

The police took Diersing, Slota and the others away for questioning. Nobody knew where Kevin was. Virginia Tech officials gave them no information, all through the long day ahead.

"They didn't tell us anything," Lois recalled Tuesday in a brief, emotional telephone call. Slota drove Linda around campus Monday looking for her husband. They spotted his car in the parking lot but couldn't find him. Slota drove Linda home to wait for more information.

Finally Lois and Linda went to the campus about 5 p.m. Monday and walked to Norris Hall, where a police officer on the scene told them that Kevin had been killed, Lois said.

"It would have been nice" if they would have been informed some other way, Lois said. But Ishwar Puri, head of their husbands' department at the university, met with them, and his warmth "very much made up" for the university's failure to communicate with them, Lois said.

The sisters, who are from Ohio, are "extremely close," said family friend Barbara Leech, a laboratory assistant at the University of Virginia who worked with Kevin Granata there. She said that Lois and her husband followed the Granatas to Blacksburg, Va., when Kevin was hired there in 2003, leaving his position at the University of Virginia. Linda is believed to have met Kevin when both were pursuing graduate degrees at Purdue University.

Slota has spent the past few days trying to reconstruct in his mind the morning's events. He has realized the attacker must have walked by their door and chained the building's entry while they were chatting that morning. Then the assailant went upstairs and continued the killing rampage he had begun at a dormitory.

He learned the rest of the story Wednesday morning in a conference and counseling session for the employees of the school's Department of Engineering Science and Mechanics, who are mourning the death of Kevin Granata and professor Liviu Librescu. There Slota, Puri and others were told that when the gunshots rang out on the second floor, Granata, a military veteran, was in his office on the third floor. He walked out and across the hall to a classroom, where 20 frightened students were wondering what to do. He directed them into his office, where he ushered them to safety — in close quarters but behind the locked doors. Then, aware that other students might be in danger on the second floor, he and another professor, Wally Grant, went downstairs to investigate, Slota said.

Cho spotted them and shot them both. Grant was wounded but survived; Granata was killed. If the students in the classroom had tried to run out, they would have confronted the killer, too, Slota said.

"All those in that class, they all made it," Slota said. "They were locked up until the police came. (Granata) couldn't sit around and do nothing. He had to help out, find out what was going on."

Leech and colleagues said Granata was a devoted family man and the kind of person who would have confronted danger to defend others.

"He was very protective," Leech said.

Both families are grief-stricken about Granata's death and have been further traumatized by the onslaught of reporters. On Tuesday, Lois Diersing was speaking disjointedly in trying to describe the day's events and the kind of man her brother-in-law had been.