(CNN)Evelyn Colon was one of five siblings in Jersey City, New Jersey, when she got pregnant in 1976 at age 15 by her 19-year-old boyfriend, Luis Sierra.
"Back then, things were a little different," said Miriam Colon-Veltman, Evelyn's niece. "It was a different culture, a different time, in the 70s. You get your girlfriend pregnant, you move out, and that's how it is."
Colon-Veltman said the couple moved into an apartment together soon thereafter and Colon's mother would often stay in touch with the two to see how they were doing. One day, though, her mother went to the apartment to visit and nobody answered the door.
"She just left," Colon-Veltman said. "People around the neighborhood, they said, 'Oh, they moved away.' So that's the story that we grew up learning."
Family members told CNN they received a letter from Sierra later saying that he and Colon were OK, but that she didn't want to have any contact with her family.
Evelyn's nephew, Luis Colon Jr., said his father -- Evelyn's brother -- told him growing up that she would reach out to the family when she was ready. "They always felt she left with him to start her new life with him and she just wanted to stay away."
The family never heard from Evelyn again.
What the family didn't know was that her body was found in 1976 but remained unidentified until Pennsylvania State Police identified the remains as Evelyn nearly 45 years later.
The details of her death, according to the National Center for Missing and Exploited Children (NCMEC), are gruesome. Evelyn's body was found dismembered in three suitcases on the banks of the Lehigh River, underneath a bridge of Interstate 80 in Carbon County, Pennsylvania, on December 20, 1976.
Evelyn was in her third trimester and her fetus, a girl, had been removed from her body and was found with her in one of the suitcases, according to the NCMEC.
Investigators in the case had given the remains the name "Beth Doe" and that how she was known until this week. In a statement sent to CNN Friday, Pennsylvania State Police said that it had both confirmed the identity of the remains as Evelyn Colon and her fetus, and arrested a suspect: Luis Sierra, Colon's boyfriend.
Sierra, now 63, was arrested and charged with one count of criminal homicide in Ozone Park, New York on March 31, where he is awaiting extradition, the statement said. No other details were released.
"Numerous interviews and investigational processes were conducted following her identification which led to the development of a suspect," according to the statement.
CNN has reached out to the Carbon County District Attorney's office to determine whether Sierra has retained an attorney.
Colon-Veltman called Trooper Brian Noll with the Pennsylvania State Police a "hero," noting that the department continually reopened the case over the last several decades.
The answer they never expected
Colon Jr. and Colon-Veltman, who are brother and sister, told CNN Saturday that the family never believed anything nefarious had happened to their aunt. The belief was that she had a family of her own and was taking care of them through the years.
But they still wanted to find out what happened to her. Colon Jr. said that his father would constantly search for her and had hoped to find her in more recent years, with the advent of the Internet and Facebook.
"I would see my grandmother, she would walk around Jersey City and look for her," he said. "'Hey, did you see Evelyn?' She would think she saw her and tell my other grandmother, 'Hey, I think I saw Evelyn!' She would say, 'I don't know why, I can't find her.'"