Tony Keller and Karmen Anderson spent hours researching together at the University of Vermont.
When Anderson graduated in May, she followed her former engineering professor to Tampa.
They again researched together and lived in the same apartment complex.
Now, Temple Terrace police want to know why Anderson's boyfriend, Corey Crandall, 22, opened fire on Keller and Anderson on Wednesday night, killing them, before turning the gun on himself in an apparent murder-suicide.
"In terms of what may have sparked this, we just don't know," said police spokesman Michael Dunn.
The shooting happened at 10:11 p.m. at the Preserve at Temple Terrace, a gated apartment complex on Fletcher Avenue where all three lived.
Off-duty Temple Terrace Officer Todd Lyons heard a volley of shots from Apartment 926, the second-floor apartment Anderson and Crandall shared at 13155 Mallard Landing. Lyons ran to the apartment and saw Crandall standing outside it, gun in hand.
Lyons shouted for Crandall to stop, but he ducked into the apartment, fatally shooting himself, police say.
Inside the apartment, police found an injured Anderson and Keller's body. Both suffered several gunshot wounds. Anderson was taken to University Community Hospital, where she died at 11:33 p.m., police say.
So far, police have no motive, Dunn said.
On Thursday morning, the couple's building smelled of cleaning supplies from crime-scene decontamination crews. Yellow police tape wrapped around a stairwell flapped in the breeze.
Lakshmi Challa, 34, lived across the hall from Anderson. He knew her only from casual hellos in the parking lot.
Challa heard the shots while he browsed online.
"I thought of calling the cops but by that time, they were here," he said. He stayed in his apartment until morning, fearful the gunman was on the loose.
A respected engineer
Just what happened between the trio seems a mystery.
Laurel Zeno, program coordinator for the Vermont Space Grant Consortium, worked with Keller at the University of Vermont.
"Dr. Keller was a family man and a very capable man and all of that," Zeno said. "Certainly I liked him as a person."
An accomplished engineer, Keller won a prestigious Fulbright Scholarship in 2004, which led him to study and lecture at Cairo University in Egypt in the spring of 2005.
According to the Burlington Free Press, Keller was struck at age 14 when he watched the first moon landing - an experience he said sparked his early interest in aeronautics.
Keller held bachelor's degrees in general engineering and general science from Oregon State University, a master's in bioengineering from the University of Washington and a doctoral degree in mechanical engineering from Vanderbilt University, according to the OSU Web site.
He spent 15 years at the University of Vermont.
Zeno also knew Anderson, whom she described as a "very lovely young woman, a very nice person."
When Keller took a job in Tampa with the Musculoskeletal Research Foundation, he offered Anderson a job, Zeno said. When she got her bachelor's degree in May, she moved to Tampa.
Zeno knew Crandall, a security guard with Allied Barton Security Services in Tampa, only as Anderson's boyfriend.
Crandall's family could not be reached for comment, and Anderson's father, Karl, declined to speak with a reporter.
'A tragic loss'
Keller's son, Jeff Keller, lives with his mother, Sally Keller, in Vermont. He told a reporter his parents had divorced. Sally Keller declined to comment.
Keller's fiancee, Kerry Sullivan, lives in Arizona. She said the couple was supposed to close on a house in Tampa on Thursday morning. "I can't even fathom it," she said of his death. "He's a good man."
Dr. Roy Sanders wooed Keller to Florida a couple of years ago, said Sanders' wife, Melanie Sanders. Sanders and Keller met years before at Vanderbilt.
"This is all very sad," she said. "It's just sad for whoever did this."
Keller's real estate agent, Mary Esther Parker, called him when he didn't show up for his closing Thursday morning.
"It's a tragic loss for his research program," Parker said. She urged the public to look online at his research. "He was a very unassuming person. He didn't brag about what he did. ... He was just a really nice guy."
Researcher Cathy Wos and staff writer Rebecca Catalanello contributed to this report. Abbie VanSickle can be reached at (813) 226-3373 or email@example.com.