Forensic experts in Mexico have found 13 bodies buried in shallow graves in northwestern Sinaloa state. Investigators said the victims had been shot in the head. Authorities were alerted to the mass graves in Sinaloa by a local farmer who noticed a strong smell coming from the field where the bodies were buried. The find comes at the same time as officials unearthed another 10 bodies in the northeastern state of Tamaulipas, bringing the total to 126 in recent days. Meanwhile, Mexican authorities have arrested 16 police officers accused of protecting drug gang hitmen who massacred people found in mass graves near the US border. Authorities have blamed the Zetas drug gang for the killings and say 17 gang members have been arrested so far.