Al Jazeera: It is more than two years since Kenyan troops went into Somalia to fight al-Shabab. Why did al-Shabab attack Nairobi now?
Sheikh Abulaziz Abu Muscab: We have been late in attacking Nairobi.
We did not attack before because they were expecting us to attack. Our aim is to attack our enemy when they least expect us to attack. This time they were not expecting us to attack.
We choose when to attack, and best time to attack.
