I think this should be "The police arrested Sami."

Quirk et al., A Comprehensive Grammar of the English Language (Longman, 1985, Section 5.29), would probably classify this use of the + police along with singular items like the Prime Minister, and plural examples like the airlines and the masses, as being part of the "larger situation (general knowledge)" in which members of the speech community know the identity of the noun being talked about. That is, if someone refers to the police or the government, no one needs to ask "Which police?" or "Which government?" because the signals shared knowledge.

In other cases, however, the plural form "police" refers to an unspecified number of (flesh-and-blood) members of the police force, as in your sentences 1, 5, and 6:

1.[Police] warned citizens to escape from the contaminated areas.

5.[Armed police] were surrounding the escaped prisoner.

6.[Swiss police] said it appeared to be an accident.



The same could be said of the next examples, although these nouns could very well be used with the as well:

2.The couple waited for [police] to arrive and told them what had happened.

3.He urged his son to surrender to [police].

4. [Police] [are] on/at his heels.

7.[Local police] want him.

Here is the difference, as I see it: When the is used, the noun police is seen as an institution. In contrast, when no (zero) article is used, the noun refers to (an unspecified number of) actual members of the police force in an actual situation.


Source: http://www.pearsonlongman.com/a...les/00347.html

Could you please translate this sentence into one of the languages you speak? I'd appreciate that very much.