Dan Probst wipes away tears as he talks about his beloved Aunt Catherine, who was a traveler who had visited 75 countries.

"We didn't expect her to last forever, but she was in real good health and it came as a shock,” Probst said.

Catherine Probst's family now believes she may be one of Billy Chemirmir's victims. Police believe he is a serial killer who attacked elderly women and stole their jewelry.

"It was one thing to suspect for two years that there had been foul play, but to know this. She didn’t deserve this,” said her niece, Jane Fold.

Catherine died on April 8, 2016, at the Edgemere Retirement Community in Dallas. Her family says the 88-year-old woman had been out to dinner with them two days before she died. They say the retired army doctor took care of herself.

"There really wasn't an explanation for her sudden death,” Probst said.

The family insisted on an autopsy when they noticed some of her belongings were missing, including jewelry, and when blood was found on her bed.

The medical examiner ruled her death was natural, but did include that her family expressed concerns about missing personal effects.

“We knew she had loose jewels. We know she had gold coins. We don't have the inventory of all that,” Fold said.

When the family saw the news of Chemirmir's arrest two weeks ago, they immediately called Dallas police.

It turns out he was arrested for criminal trespass at Edgemere in April of 2016. The same place and around the same time Catherine Probst died.

“We convinced ourselves after the autopsy that maybe she died peacefully in her sleep, and you console yourself with that, but murdered is just unbelievable," Fold said.

Dallas police and the medical examiner's office are now reviewing Catherine's case and may change the ruling of her death to murder.

They are also reviewing more than 750 cases of elderly women who died of natural causes or unexplained deaths. For now, Chemirmir has only been charged in one murder and one aggravated assault, but sources say they suspect him in at least nine murders.

WFAA obtained a search warrant of Chemirmir’s house. Among some of the things police recovered were jewelry and cell phones.