PLANTATION (CBS4) – As the investigation continues into what drove a Connecticut man to open fire in an elementary school, killing 20 children and six adults, many people struggle to comprehend why.

South Florida forensic psychologist Harley Stock, who has trained the FBI in criminal profiling, said there had to have been signs prior to the shootings.

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“These kind of individuals tend to signal things. They generally have problems that are recognizable. I suspect that family knew there was something wrong with him, he may have even talked about killing,” Stock told CBS4 Chief Investigator Michele Gillen.

Surely, he believes, a trail of red flags will be uncovered in what might be professional deemed interpersonal targeted violence.

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“This is a horrible event. But let’s be clear, this is not a school shooting this is a shooting at a school,” said Stock,

Stock explained that at this point, the murder of his mother- who happens to be a teacher – colors the investigation and definition of what the worst mass shooting at an elementary school in American history.

“A big question will be what did the mother know in advance, if anything,” said Stock.

He said the cases were children so young are killed is rare, and that when it does happen it means the killer has broken from any moral compass.

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In the end, Harley says such overwhelming grief will forever be etched in the soul of this community.