"The police needs the documents of the tourist"
Translation:Polisi anahitaji nyaraka za mtalii
"The police needs" is not correct English. You can say "the policeman/woman needs" or "the police officer needs .." Or if you don't wish to refer to a single individual, then "the Police need ..." I might have added a verb kuona/kukagua or something like that. "Polisi anahitaji kukagua nyaraka ..."