Prosecutors in Michigan on Thursday accused James Crumbley of failing to secure the gun that his son used to open fire in a high school hallway and kill four students — one of several ways they say he could have stopped the deadliest school shooting in state history.“Those kids would still be alive today had James Crumbley seized any one of the tragically small and easy opportunities given to him to prevent his son from committing murder,” Marc Keast, an Oakland County prosecutor, said in opening statements.The cable lock for the 9-millimeter Sig Sauer handgun that Mr. Crumbley…