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CNN) -- What's clear: Katherine Russell claims she was completely in the dark about her husband's alleged plan to bomb the Boston Marathon on April 15.
What's unclear: How could she not know?
Russell and Tamerlan Tsarnaev were married on June 21, 2010. She was raised in a Christian household in North Kingstown, Rhode Island, but converted to Islam after meeting her husband while attending Suffolk University.
She worked as a home health aide and would often leave their toddler daughter with her husband while she went to work.
"The reports of involvement by her husband and brother-in-law came as an absolute shock ..." Russell's lawyer said in a statement. "As a mother, a sister, a daughter, a wife, Katie deeply mourns the pain and loss to innocent victims -- students, law enforcement, families and our community."
There are plenty of open questions surrounding the Tsarnaev brothers' alleged terrorist plot, but this one is glaring: How did Katherine Russell miss signs that her husband was poised to dive off the deep end?
When we think "double life," we think about affairs, tax evasion, even pedophilia and rape, says Dr. Gail Saltz, the author of "Anatomy of a Secret Life: The Psychology of Living a Lie," but in the United States a terror plot seems relatively far-fetched.
Pop-psych bonus: How to tell if your spouse is in training to become a mad bomber:
Psychology experts say that while the signs vary depending on the nature of the "secret life," there are clear markers to look for in a loved one who might be harboring violent or harmful tendencies.
These include, but are not limited to: moody outbursts, paranoia, hidden financial transactions, increasing extremism, emotional abandonment and complaints of feeling victimized.