>> reporter: luken discovered darker secrets as well. john supplied the opioids that killed his own addicted brother. he was alone with his sick father when the old man died rather suddenly. john wasn't charged in those cases, but there were others, said luken, and as the years went on, he developed a certain criminal specialty. >> he would go on dating websites and he would find women that usually had good financial backing. he always told people he was a doctor. >> reporter: he seemed like an ideal catch, i suppose. >> yes. >> reporter: for a lot of these women. >> he was a true con man. he'd take their money and when they would find out about him john would threaten them, he would terrorize them. >> reporter: how bad was he? >> john was the most dangerous, treacherous, manipulative, deceitful criminal that i'd investigated in 40 years of law enforcement. >> reporter: once terra learned about john's past, she was consumed with worry.