Three civilian bystanders and one policeman were killed, and six other people were wounded.Al-Qaida in Iraq and other militant groups have been gathering strength in and around Mosul, some 360 kilometers (220 miles) northwest of Baghdad.In the city of Tuz Khormato, 210 kilometers (130 miles) north of Baghdad, gunmen on motorcycles riddled a civilian vehicle carrying four off-duty policemen with bu