Learn French: La police parle d'un meurtre. - The police are speaking of a murder.

In French, la police is a singular collective noun, referring to the institution as a whole. Therefore, it always takes a third-person singular verb (la police parle). If you want to talk about multiple individual police officers, you would use the plural les policiers.

Since this lesson is about unconfirmed news (the journalistic conditional), why isn't parle in the conditional tense?

The journalistic conditional is used for facts the speaker isn't 100% sure about. In this sentence, the fact that the police are speaking is a confirmed certainty, so it uses the present tense (parle). If the reporter wanted to express that the event is allegedly a murder, they would use the conditional to describe the crime itself, such as Ce serait un meurtre (It is allegedly a murder).

Why is it d'un meurtre instead of just un meurtre?

The verb parler requires the preposition de when you are talking about something. So, parler de means "to speak of" or "to talk about". Before the vowel sound in un, de drops its 'e' and becomes d'.