Sounds much like another Mumbai-style group terror attack. Mumbai was on 26 November of 2008, almost 5 years, coincidental?
Remember, the attacker can look at many targets and select time and place of the attack and concentrate his forces for that occasion. The defenders must monitor all targets, not be distracted or get bored and respond instantly wherever and whenever the attack comes.
Shopping areas, malls, transportation hubs and sporting venues are security nightmares all over the world!
Success copies success. Al Shabaab has Somali supporters in the USA. No good turn goes unpunished.