SHERMAN, Texas (KTEN) —  On September 20, 2010, a fire broke out at a mobile home on Reynolds Road, west of Sherman.

Police and firefighters arrived to find Brian Ritchie and sisters Misty Ballou and Cassandra Ballou — who was pregnant — dead at the scene.

A medical examiner's report determined that all three of the adults had been shot and two had been stabbed prior to the fire, which was set by an arsonist.

Over the course of the following 13 years, investigators have continued their search for the killer or killers.

"Everybody that has kind of gone through CID and worked in investigations, and everything has tried to add a piece to the investigation to keep it moving forward," said Grayson County Sheriff's Office Capt. Marty Hall.

Since that dark day in 2010, both technology and the personnel working the case have changed.

"We've been hampered by technology," Hall said. "There are more things that are available today that weren't available then."

In the last year, Lt. Mark Kosemund has taken the reins of this cold case.

"You're having to go back through the entire case file... seeing where they are, seeing what leads they've chased down, seeing what leads had alibis and that stuff," he said. "And then you're also developing your own stuff at the same time."

Part of the reason cold cases take so much time, according to the sheriff's office, is the volume of information that investigators continue to digest.

"You have to treat every piece of information as though it's valid," Hall said. "So we have to go forward with everything we can, and so unfortunately, that's where it can get clouded and it does take time."

Investigators hope each step further into the case brings them closer to an answer.

"Do a lot of footwork, do some interviews, we might finally have someone who's willing to come forward, give a statement or something if they have information," Hall said. "We spend time writing all that stuff down."

No matter what frustrations the sheriff's office finds in their search, the victims' loved ones are first on their minds.

"Keep working till we get closure on it," Hall said. "Get closure to the families."

He adds that investigators remain in touch with the families a few times a year to let them know where the case stands, so loved ones are aware the sheriff's office hasn't lost hope.