DALLAS (CBSDFW.COM) – The mass shootings in El Paso and Dayton, Ohio this past weekend have highlighted the challenges law enforcement face with stopping domestic terrorists.

A little more than a week ago, FBI Director Christopher Wray warned about the threat of domestic terrorists.

A criminology expert told CBS 11 News, the threat is growing quicker than law enforcement is prepared to keep up with.

The FBI has more than 850 open domestic violence investigation, but individuals still often go undetected until it’s too late.

Despite having uploaded a hate-filled manifesto to the site 8chan prior to his attack, it appears the El Paso gunman Patrick Crusius was not on the radar of law enforcement.

“I think we are going to see more of that,” said Dr. Alex del Carmen, a criminology expert at Tarleton State University. “I don’t think law enforcement is able to identify them on an ongoing basis in a proactive manner.”

He said the problem is law enforcement doesn’t have enough manpower or resources to track and identify legitimate threats online.

“The most depressing thought is we are not giving them the tools they need in order to be able to do the job that they are required to do,” del Carmen said.

In the next ten years, del Carmen said domestic terrorists will pose a greater risk for the safety of Americans than foreign terrorists.

“What I can tell you right now is there are people currently planning another attack,” he said. “What we need to try to understand is who these people are, how serious they are about doing harm to others, and be able to get to them before they actually engage in that harm.”