Earlier this summer, after more than a decade of alleged sex abuse, the high school student told her family about her grandfather.

The 17-year-old wasn’t as concerned for her own well-being, her mother said, as that of her young cousins. The little girls were 1 and 3, about the age she was when the abuse began, the girl told police.

The teen told her story, and police investigated. Mark K. Kleinsorge, 64, was indicted last week in Charles County on 27 counts related to sexually abusing the teen. He was also charged with five similar counts in North Port, Fla., where Kleinsorge had moved and the abuse allegedly continued in recent years.

Kleinsorge, a longtime employee of NASA’s D.C. office, was arrested Wednesday in Florida on the Maryland charges. He is being returned to Charles for arraignment.

Megan Coleman, a lawyer who expects to represent Kleinsorge in Maryland, said he denies the charges and will fight them in court. Reached at home, Kleinsorge’s wife declined to comment.

Now other members of Kleinsorge’s family are grappling with his alleged betrayal.

“Whatever the universe can do to me is nothing compared to this,” said the teen’s mother, a 45-year-old who works in the computer field. “All you really want to do is undo it.”

The Washington Post generally does not name victims of sexual abuse or their relatives if doing so would identify the victim.

Police in Charles want to know whether there are other victims. They do not have specific information, but their general view is that people who sexually abuse children often have multiple victims.

“It’s very difficult for victims to come forward,” said county police spokeswoman Diane Richardson. “But if there are other victims, we need to hear from them.”

According to a North Port police report, the abuse — which sometimes was committed in Kleinsorge’s bed — occurred from the time the girl was about 3 year old to age 14. It included touching and the child performing sex acts on the adult, her mother said.

The girl called Kleinsorge, her step-grandfather, “Pop.” He had always been in her life. He and the girl’s grandmother, who married in the late 1980s, lived near the girl in Charles, and would frequently babysit, take her to their home for weekends and, when she got older, host her for a week each spring at their Florida house.

Some of the alleged abuse happened when Kleinsorge took the girl, then a toddler, to his office in downtown Washington for “take your daughter to work day,” the mother said. He has since retired.

The charges in Charles include multiple counts of parental child abuse, child sex abuse and third-degree sex offense. In Florida, Kleinsorge is charged with two counts of molestation of a victim under 12, and three counts of lewd or lascivious conduct by a person over 18.

All of the counts against Kleinsorge relate to the same victim, according to authorities.

A court date has not yet been set.

The girl’s mother said the family is steeling itself for the legal process. It is her belief that her daughter coming forward might have spared other young relatives.

She said that hearing her daughter’s story has been heartbreaking, but that it has increased her understanding as a mother.

The girl has struggled in school for years, her mother said, and seemed to have emotional barriers. Since she began talking about the alleged abuse, the girl has softened and opened up, her mother said.

“She had this weight on her,” said the girl’s mother, her voice catching with emotion. “Now that it’s lifted, I’m getting to see some of her sweetness and joy. I’m getting my little girl back.”