PORTLAND, Ore. — The deadly shooting last week at an Oregon community college has an eerie parallel with the massacre at Sandy Hook Elementary School that killed 20 pupils and six adult staff members in 2012.

Like Adam Lanza, the gunman in the Connecticut massacre, Christopher Harper-Mercer was living a mostly solitary life with a mom who shared his fascination with firearms.

Both stories illustrate the struggles parents face caring for a deeply troubled child, struggles that can inadvertently lead to a volatile outcome made easier by ready access to weaponry.

“When you begin to bring guns into the home environment where you have that dangerous cocktail of behavior, that’s pretty unbelievable,” said Mary Ellen O’Toole, a former FBI profiler who directs George Mason University’s forensic science program.

Harper-Mercer bears similarities to other school shooters: a young male focused on mass lethality and carrying out the killings in a military-like mission destined to end in the killer’s own death, O’Toole said.