Columbia, Md (WUSA9) — The man who killed three innocent bystanders during a senseless outbreak of domestic violence in Brookeville, Md. on Monday was a mentally unstable con man who was struggling with drug use as well as marital and financial problems, according to a former co-worker.

"He was unstable," said Brandon Halstead, and Army veteran and self-defense instructor who served in Afghanistan and later worked with Christopher W. Snyder at the Code 3 Tactical Academy in Columbia, Md.

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Halstead said Snyder often talked about a shadowy background in the military and work for government security contractors overseas, but could never provide convincing evidence when challenged on details.

"A lot of the things he said seemed pretty far fetched," Halstead said.

Even so Snyder would sometimes flash a credential or show off a training weapon that appeared to indicate he might have some link to government service or armed security contracting overseas. Co-workers never pressed Snyder further Halstead said.

Halstead called Snyder a "con man".

Over time, Halstead said he found Snyder to be a deceitful and angry person.

Halstead claims Snyder appeared to have serious mental health problems and had talked about his drug use including steroids, prescription opiods and stimulants.

Snyder was struggling with a failing marriage and was having financial problems in his business, Halstead said.

"It all just came together into this perfect trifecta for somebody this unstable to have a mental breakdown," Halstead said.

Synder killed three people after bursting into the home of a neighbor on Monday. Snyder's wife had fled to the home claiming she had been held hostage by Snyder in their nearby home over the weekend. Snyder's wife survived the attack.

Snyder killed himself after retreating back to his house and engaging in a seven-hour standoff with police.

Snyder was the holder of a federal firearms dealer license and had an extensive gun collection in his house, Halstead said.

Snyder is described as the Chief Instructor for the Code 3 Tactical Academy in an on-line profile. The profile says Snyder has 22 years of security experience including in the military and as a contractor.

Code 3 Tactical Academy's Facebook Page features videos of Snyder demonstrating self-defense techniques including how to disarm attackers.