The FBI and Department of Justice should consider the results of the case of the German Operation Pastorius in 1942 when dealing with present day terrorist.
Operation Pastorius was an attempt to have two, four man teams destroy infrastructure in the United States in the summer of 1942. The team that landed on Long Island was immediately noticed by a Coast Guard Seaman who raised the alert. The resulting manhunt resulted in the saboteurs turning themselves in. Two of the team cooperated and informed the FBI about another team operating in Florida. Within weeks that team was captured and all eight men were tried before a military tribunal and sentenced to death.
The two who cooperated were commuted to life in Federal Prison by President Roosevelt. From landing to electric chair, less than two months. The two surviving saboteurs were deported in 1948.