HOUSTON — A retired FBI special agent, lawyer and former prosecutor said “calculated luck” is a big part of cracking weeks old missing persons’ cases like that of Maleah Davis. 

Dennis Franks, who was a prosecutor in North Carolina and spent 22 years as a Supervisory Special Agent for the FBI, said investigators have to create opportunities for luck to develop.

“At some point you’ve exhausted all leads,” he said. “You’re looking for any (tip) at all. Don’t discount anything. Keep (the case) alive. Keep it going. It may take six months. It may take a year. It may take two years. So what (Houston Police Chief Art Acevedo) is doing here is very important.”

The chief is pushing to keep the case public.

Maleah was last seen 23 days ago. Police no longer think she is alive. Her stepdad Derion Vence is their only known suspect. 

Vence is already in jail accused of tampering. If he knows where to find Maleah, he will not tell investigators, police said.

So they are relying on tips and released photos to get good ones.  Two weeks ago, authorities shared a photo of a gas can found in Vence’s car trunk. Detectives want to speak with whoever sold it to him.

In that same car trunk, police dogs caught whiffs of human remains.

While investigators wade through forensic test results, Chief Acevedo spoke out hoping continued publicity on the case helps bring forward a witness.

RELATED: Reward for finding Maleah Davis increases to $20,000

“Anybody that might have seen something suspicious involving an individual that matches the description of the step father we’d want to know that,” he said.

Chief Acevedo believes a break is close. To get it, Franks said detectives could  eventually release details they have been too hesitant to share with the public.

RELATED: Houston Police need your help with tips in Maleah Davis case

“The longer (the case goes unsolved) the more likely there is that things will be disclosed,” Franks said.

RELATED: 'We need to bring her home' | Houston Police Chief makes impassioned plea to find Maleah Davis

WATCH: Tips starting to dry up in case of Maleah Davis' appearance

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