I so agree with the welding torch as being a sign that this is not a first for her.
Agree with you. Also, the homicide detective is both seasoned and interviewed her:
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http://www.khou.com/news/Police-Woman-charged-in-boys-death-a-cold-soulless-murderer-112682194.html
I was one of the detectives to interview Mona Nelson, and I can tell you that she is a cold, soulless murderer who showed an absolute lack of remorse in taking the life of Jonathan Foster," HPD Homicide Det. Michael Miller said.
And...
Miller said. "I’ve worked in the homicide division for 14 years and this is the worst case that I’ve been a part of."
And it appears to be his opinion that:
"Do I believe she’s done it before? Yeah, I do. I don’t believe she began and ended with the abduction of Jonathan Foster," Miller said.