Why did Florida man kill daughter, 6 grandkids?

UPDATE:  Cops say that what drove killer grandpa Don Spirit, 51, to murder his daughter and six grandchildren remains a mystery. Spirit allegedly called 911 saying he had "injured someone."   
His daughter was identified as Sarah Spirit, 28, according to local news reports.
 Sheriff's Office named the six children Thursday: 3-month-old Alana Stewart, 4-year-old Brandon Stewart, 5-year-old Destiny Stewart, 8-year-old Johnathon Kuhlmann, 9-year-old Kylie Kuhlmann and 11-year-old Kaleb Kuhlmann.
According to the New York Daily News: "In 2003, the Orlando Sentinel reported, a man named Don Spirit, then 40, pleaded guilty to being a convicted felon in possession of a firearm after accidentally shooting to death his 8-year-old son during a hunting trip two years earlier. The boy, named Kyle, was shot in the head when his father's high-powered Browning rifle went off while the dad was pointing out a rust spot. "


EARLIER: A Florida man, 51,  shot his daughter to death then murdered his six grandchildren before blowing his brains out Thursday. Cops say they received a call from the family home in the small town of Bell but when they arrived, everyone was dead. Don Spirit, 51, has been fingered by detectives as the triggerman -- and he has a criminal record and they had answered calls to the house "numerous times."
Bell is in Gilchrist County, south of Gainesville and has just 350 people. The children ranged in age from 3 months to 10-years-old.