NORTH RICHLAND HILLS (CBSDFW.COM) – It is a murder that has gone unsolved for four years.  Shortly after dinner on the night of December 9, 2007, someone knocked on Marianne Wilkinson’s door in North Richland Hills while her husband watched TV.

When she answered the door, someone shot her.

Now, her family believes an arrest may finally be on the horizon.   “I’m confident they’ll solve it,” says son Mike Wilkinson,  “I think we’re close, based on what the police department tells us.”

Daughter-in-Law Terri Wilkinson echoes her husband’s hope.  “I am optimistic one day there’ll be an arrest and the right people involved will be held accountable.”

The Wilkinsons feel police are on the brink of solving the murder based on information no one wants to reveal.  They’ve felt close before; like when the murder weapon was eventually found, and then a breakthrough forensic method revealed a fingerprint from a shell casing that had been wiped clean.

No prints matched, but the family remains hopeful….and anxious.  “I guess I’m anticipating going through some more grief again knowing that they’ve caught the person or people responsible,” Mike says.

Police won’t say if Wilkinson was the intended target, but they don’t believe it was a random shooting.

“I do believe there are individuals out there that know what occurred and why it occurred,” says North Richland Hills Police Investigator Keith Bauman.  “It could’ve been she simply was at the wrong place at the wrong time.  There are theories, but we really can’t go into theories until we have sound facts of what happened.”

There’s nothing of the Wilkinsons left at the house where the shooting occurred; her husband moved to be closer to one of their children.  But her life is still celebrated in subtle, joyful ways.

Every Christmas the family adds a new ornament to the tree in her memory, like a dove made the year Wilkinson died. Likewise, on her birthday, they release a balloon to the heavens, a tradition that began on the first birthday following Marianne’s death.

“I kind of dreaded that first birthday,” says Terri.  But then the family shifted its focus.  “’Hey, this is her first birthday in heaven.’   So we released one balloon, so each year on her birthday we release one balloon, and when we do we have to tell memories about her.  Yes, we’re sorrowful but we keep those joyous times of the things she did that touched us deeply… alive.”

And they pray that people who know what happened to Marianne Wilkinson find the courage to go to police.  “That’s our prayer that those that were involved have to be held accountable for what they did, Terri says, “and pray, too, for those people who know what happened and might be afraid to come forward and say anything…that they find the courage deep within to tell what they do know.”

She says there will never be what people popularly refer to as closure.  “But our sense of justice and right and wrong will let us move to a new level of closing.   Once we know what happened and those that did that are held responsible.”