Gary Ray Bowles, who went on an eight-month killing spree that left six dead in 1994, apologized in a statement before his death by lethal injection.
A co-worker reported the alleged threat to officials and police say they found multiple firearms at the suspect's home.
The store's interior will be entirely new, and a memorial will be featured to honor those who were slain in the mass shooting.
More than 146,368 square miles, or an area equivalent to the size of Montana, had been searched, the Coast Guard said.
The boy was bitten on the head and is in serious but stable condition. An official said his father saved his life by scaring the mountain lion away.
