Castro had reportedly spent this month on suicide watch at the Ohio Correctional Reception Center. He was kept away from the general prison population (for obvious reasons), and guards checked on him every 30 minutes. Apparently, during that time frame, Castro managed to construct a noose with his bed sheets. His body was later found during a security check.
This ends an unbelievably awful story that began last May, when neighbor Charles Ramsey found the three missing girls held captive in Castro's home. It's shitty that Castro got to go out on his own terms—he deserved much more than a hanging—but, hopefully, the three women will be able to find some peace now that he's gone.