Police released images of how an attacker connected to several crimes, including at least a rape and a murder that happened more than 20 years ago in Montgomery County, Md., might have looked at 25 years old, left, and at 45 years old. (Courtesy of Montgomery County Police)

On a fall night 24 years ago, research biologist Le Bich-Thuy boarded a Metro train in the District, exited at the Twinbrook station in Rockville, and walked home.

Bich-Thuy never made it. Someone followed her and dragged her into a side yard. She was raped, battered with a piece of concrete and strangled. The case remains unsolved.

Now, though, Montgomery County investigators say they have a rough idea of what the attacker may have looked like, because of an emerging forensic technique called “DNA phenotyping” that projects genetic clues left at crime scenes into facial images. On Monday, they released images of how the man might have appeared at 25 and 45.

“We’re looking for any new information, anything these images might prompt someone to remember,” said Sgt. Chris Homrock, head of Montgomery’s cold-case squad.

Unlike past cases in Montgomery County, when detectives employed the imaging technique, this time they were able to use identical DNA collected from two crime scenes. The other case dates to 1989, five years before the scientist was killed, and involved a woman raped after she, too, exited the Twinbrook station and headed home.

DNA at the scene in 1994 matched DNA from the 1989 crime scene, and Homrock is convinced the same man committed both crimes. Homrock also strongly suspects the man attacked other women. “I don’t think he did this just two or three times. This guy was targeting women in that area for at least five years,” Homrock said.

The sergeant and his detectives have examined two other crimes reported near the Twinbrook Metro station from that time — including an attempted rape, in 1994, by an attacker armed with a knife whom the victim fought off. The common denominator, Homrock said, was a victim who had just left the station and was probably followed — either as she walked home or took a short bus ride. Then the man would spring out just before the victim got into her residence.

“The common theme of these cases is they all start at the Twinbrook Metro,” he said. “Everything generates from there.”

Bich-Thuy lived by herself in a house on Martha Terrace. The molecular biologist had relocated from France and had been working at Children’s National Medical Center. One of her projects involved pediatric pulmonary medicine. The well-liked 42-year-old also played cello in a community orchestra.

“She just was a wonderful person. When she smiled, the room lit up,” Ervin Klinkon, director of the Montgomery College Symphony Orchestra, told The Washington Post in 1994.

The DNA phenotyping images, generated by Virginia-based Parabon NanoLabs, rely heavily on genetic histories linked to the DNA found at crime scenes. In this case, that has led detectives to know, fairly confidently, that the assailant is white, has blue eyes and no freckles, and has a distinctive shape to his head, Homrock said.

But the technique has limits. One big one: There is no way, based on the genetic markers to know the age of the attacker, Homrock said. That is why two images were made with a 20-year age spread. Nor can the technique account for hairstyle, scars and how much a person’s appearance may have aged from smoking, drinking and diet.

Montgomery police officials term the images “scientific approximations” of appearances, rather than replicas that may help lead to the attacker.

The three crimes investigators think were committed by the same man:

On June 25, 1989, about 10:15 p.m., a 52-year-old woman was walking on Lewis Avenue when a man approached from behind, dragged her into a yard and raped her. Investigators collected evidence at the scene, stored it and years later — through scientific advances — used it as a source of suspect DNA.

On Sept. 19, 1994, about 10:20 p.m., a 25-year-old woman was walking on Twinbrook Parkway when a man approached from behind, armed with a knife. He dragged her to the side of her residence and tried to rape her. She resisted, fled and contacted police. Investigators have never been able to draw DNA from evidence at this crime scene.

On Oct. 3, 1994, the body of Bich-Thuy was found on the side of her home, and it was later determined she had been attacked several days earlier. Police had been called to her home after worried friends and co-workers hadn’t seen her.