SPRINGFIELD, Mo. -- Greene County Sheriff Jim Arnott says two people of interest in the Willinghams murder case are in custody on unrelated charges.  He updated the investigation at a news conference on Friday morning.  One of the persons of interest was arrested within 72 hours of the murders of Don and Helen Willingham, another later.

Several of the Willinghams' family members were present at the Greene County Sheriff's office on Friday morning. 

"You have to keep working, you have to keep dealing on a daily basis, and sometimes it's not easy.  But we are a family of great faith, and I am very very grateful of that- that I do have that faith, and I do know Mom and Dad are rejoicing at the feet of Jesus even as we speak right now.  That's the only way we could get through this," said Donna Willingham, daughter of the murdered couple.

The sheriff says they have received 17 of 519 pieces of evidence back from the crime lab.  Two important pieces of evidence have been sent to the FBI crime lab in Virginia. Other pieces of evidence are going back to the state crime lab fur further analysis, while some others are going to another federal lab.  Eight of the more than 100 people interviewed in the case have provided key information in the case. However, others refuse to talk with investigators. 

"They know who they are, and we know they know, and they just won't for whatever reason, and they just won't do what they should do," said Dave Willingham, the couple's son.

Arnott is pleading for anyone with more information to come forward, whether it be because of their conscience or the money.  There is $20,000 in reward money available in the case.  Call (417)868-4040, Crimestoppers at 869-TIPS, or go to the Greene County Sheriff's website to submit a tip.

"We have identified several individuals in this case that have information and choose not to speak with us, because they fear the individual or individuals involved in this case," said Arnott.

"I know that God knows who it is, and his justice is always just and righteous, and he is a vengeful God," said Donna. 

But they also know, if the right people step forward, justice could be done now.

Donald and Helen Willingham were found murdered in their home in the 2919 block of West Swan Street on April 25.  At 5:44 a.m., Helen called 911 to report someone was inside their home and assaulting Donald. 

When officers arrived, both Helen and Donald were dead.  Autopsies showed the couple had been stabbed multiple times.  Arnott says he still believes the murders were random.