Why does Álex say "A Sara la mataron"?

Question

Ok, I meant to ask earlier, but when I heard this same phrase for the third or fourth time while watching "¿Quién mató a Sara?" it just really started bugging me: this seems to be a great example of the impersonal ellos form (the whole premise is that he thinks she was killed but doesn't actually know who did it!) but I can't understand why that "la" is there. "La mataron" or "A Sara Mataron" I get, but how isn't it redundant to have both...?

If anyone knows what's going on here, thanks in advance for any insight you're willing to offer! (but no spoilers please!) 😂

Accepted Answer

Hola Sky
This is to do with the repetition of direct object pronouns that is natural and most of the time necessary in Spanish. Here's a Kwiziq lesson about this. 
And, yes, that's definitely an impersonal sentence using the 3rd person plural form of the verb. 
Saludos
Inma