Marianne Wilkinson was the apple of her family's eye -- a wife, mother and doting grandmother, known for her decorating sense and her sense of humor.

"She really made life special," says her son, Mike Wilkinson.

It's her why death has been so hard to understand for Mike, his wife Terri, and their entire extended family.

"For someone who was really that kind and that gentle to have their life taken that way-- that bothers you," Mike says.

It was 10 years ago this week that Marianne's life ended when her doorbell rang at her North Richland Hills home on Spence Court. She'd been watching TV with her husband.

"When she answered the door, she was immediately shot by an assailant and died there at the house," says NRHPD Chief Jimmy Perdue.

Perdue says his department believes this was likely a case of mistaken identity in which the shooter went to the wrong house. A lack of evidence over the years has stalled the case.

"We have some theories. We have some ideas we believe how it happened, but we’ve not been able to go to fruition," Perdue says, adding that his officers have spent thousands of hours investigating this case.

Not to mention the crime happened in 2007, long before home surveillance systems and cameras were a commonality.

"We did search every camera we knew in existence, some of the cameras on the freeways—but we just could never find anything," Perdue says.

But they've never stopped looking.

"I can't tell you how much it means to me that you’ve taken this as personally as we’ve taken it," Mike Wilkinson said Thursday, as he, his family and police gathered outside NRHPD.

"We’ll never forget, and we’ll never stop trying," Chief Perdue said to the family.

To honor Marianne's life, they released dozens of red balloons into the sky. And this holiday season, they hope whoever's responsible might find it in them to come forward and help heal this family's broken heart.

"I don’t think there’s ever closure because you're a different person," Terri Wilkinson says. "But a restfulness would be nice."