Sci-Fi story, the hero goes off on a mission that will take weeks to months. He has just left knowing his father was killed but the mercenary organization the hero works for will be strongly helping the investigation. Hero knows he'll get good answers when he gets back.

The issue is the prime suspect; the girl the hero wants to marry. So the reader knows what the hero does not; the prime suspect.

How would you, as a reader, feel about this?

I think it would depend on how you present the information - how do the readers know that the prime suspect is the girl the hero wants to marry?

On a side note, I think it would make for good drama.

I think that's definitely going to give good reader tension. Like Balec said, though, the reader's reaction will depend on how that information is presented. I think automatically you have good tension with that scenario, but I think if you put this girl in danger because she is the suspect (and seed hints that she is innocent, which I'm assuming she is) then the reader will be screaming for the hero to come back and rescue his significant andclear up the murder. Simultaneous to this, you could have the mission endanger the hero so your readers are worried he won't ever be able to come back and clear the girl from suspicion.
That setup seems to be perhaps a little common to me, but it is definitely a high reader tension scenario. I have no idea how that would work in the story you're writing, though, so it's totally just an thought...

Areth.