Mary Ann Shepherd's son Robbie Payne, 19, died Oct. 28, 1995, in a Whitestown, Indiana house fire.
Officials initially suspected arson and homicide, but no arrest was ever made.
"I feel upset, helpless, sick to my stomach and I'm trying very hard not to feel hopeless," Shepherd wrote in an email to Call 6 Investigator Kara Kenney. "It just eats away at me every day. I'm trying to stay positive gets harder and harder as the days, weeks and months go by."
Three years ago, a tip came in that reopened the investigation, and fire investigators from Lebanon Fire, Whitestown Police and the Indiana State Fire Marshal began tracking down leads.
"We've literally had to travel the Midwest to find people to interview," Chief Jason Lee, of the Lebanon Fire Department, said in 2013. "We've spent 2,000 or 3,000 man hours on this case."
Lee told Call 6 Investigator Kara Kenney they've identified suspects in Payne's death and in December 2012, they forwarded their case to the Boone County Prosecutor's Office.
"We submitted our paperwork," Lee said in 2013. "We're talking a thousand documents. Hopefully we'll get somebody put behind bars."
Payne's mother told Kenney the documents include confessions.
Shepherd said she met with Lori Schein, chief deputy prosecutor for the Boone County Prosecutor's Office, last week and was told the office did not feel it could get a conviction because of the credibility of the suspect that confessed.
"I asked her if we could bring in a third party to look at the case and give their opinion, or if we could request a special prosecutor to handle the case," Shepherd said. "I would think a confession would be a prosecutor's dream to have that kind of evidence."
Shepherd said she is still waiting to hear back on her request for a special prosecutor or independent review.
Schein told the Call 6 Investigators the office is still reviewing the case and no determination has been made on whether charges will be filed.
Whitestown Police Chief Dennis Anderson said he is also frustrated with the lack of charges filed in Payne's death.
"I think we've gone above and beyond (in investigating Payne's death)," Anderson said in 2013, expressing frustration to RTV6 at the lack of communication from the prosecutor's office. "We've gotten better cooperation from agencies outside our state than from our own prosecutor."
Shepherd said after her son died, the case appeared to go dormant.
"I've wondered if I would ever get answers," she said in 2013. "I didn't know if I was going to go to my grave never knowing what happened, until that tip came in two years ago."
Shepherd expressed gratitude toward fire investigators who've devoted thousands of hours tracking down leads.
"I won't quit trying until I can no longer try," Shepherd said. "I will keep trying to get justice for my son."