Nairobi - A Tanzanian journalist who reported on a string of murders of officials and police has been missing for the past two weeks, the two newspapers he works for have said.Azory Gwanda, a reporter for the Mwananchi and The Citizen newspapers, wrote several articles investigating attacks in Kibiti district in Pwani province, which surrounds Tanzania's main city of Dar es Salaam.Some 10 police officers and a similar number of local administrative officials have been killed by mystery motorbike attackers.Gwanda's wife said he vanished on November 21, after he left in a white Toyota Land Cruiser with unknown people on an "emergency trip", telling her he would return the following evening."She became alarmed after he failed to return home and all his numbers could not be (reached) since the day he departed," the newspapers said in a statement on Monday.Police are investigating the case. The newspapers, part of the East African Nation Media Group, called on them to "speed up the investigation."Police say they have now broken up the gang of motorcycle assassins. The motives behind the attacks remained unclear, although President John Magufuli hinted in June the attacks might have been religiously motivated, with some blaming Islamic extremists.