The police ____(try) to find out who murdered the old man now

The police ____(try) to find out who murdered the old man now

is trying

now 因为有此词,所以是进行时.
is trying
警方,用单数就行.
因为不强调个人.

The police _is trying___(try) to find out who murdered the old man now
希望能够帮到楼主