GARISSA - Two Kenyan police officers were shot dead and their rifles stolen on Sunday in the northern town of Garissa near the border with Somalia, police said.The killings came hours after a nine-year-old boy was killed in the capital Nairobi by a grenade attack on a church by suspected sympathizers of Somali al Shabaab rebels and days after Kenyan troops led an offensive against the insurgents in their last stronghold in Somalia.