Both are incredibly ego-centric acts. And profoundly dualistic.
Suicide: if you won't do what I want, I will kill myself.
Murder: if you won't do what I want, I will kill you.
That's the essence of each. Each act is an attempt to coerce the "other".
The way I see it, murder and suicide are a whole lot more complicated than you allow in your premise. People commit these acts for a variety of reasons, some of them I think coincide with your supposition, but there are a whole lot of other possibilities.
What of a person who has been bullied and made so miserable that they simply don't want to continue living anymore? I can easily contemplate situations where a person wants to die for no other reason than to end their suffering. It may very well have nothing to do with trying to hurt others or anything like that. I can even contemplate suicide where a person wants to relieve others of their suffering - say a terminally ill person who thinks they are a burden on those who love them. Similarly, what of a person who sacrifices themselves to save others - I'm sure you can google and find reports for the Medal Of Honor given out in the U.S. to people who distinguished themselves in war - you might be surprised at how many guys got the medal posthumously for jumping on grenades, killing themselves but saving others. The impulse to jump on the grenades may have been preconceived in some instances, but the instantaneous need to act in such situations suggests that altruistic intent lay behind the decision rather than self-murder for some malevolent reason.
I can think of situations where a person might kill another, not out of some egotistical assertion of power, but to save others. There is a jataka tale about the Buddha who as a bodhisattva was on a ship and found out that a pirate intended to kill everyone on board. The Buddha killed the pirate before he could act. The Buddha saved all the people on the ship AND saved the pirate from committing many murders and incurring the stain of those acts. Its a fairy-tale, but I think resonates because we could imagine it really happening especially in this post 9-11 world. What about Dr. Kevorkian who all but killed his terminally ill patients by providing them with the facilities to end their own lives? I recall when I was a kid, standing outside a bee hive and wacking bees out of the air with a stick. I had no intention of killing - I just did it because it was fun.
There is a story in the Pali Suttas recounting how a bunch of arhats killed themselves. Rather than reproach, the Buddha said it was OK because they did nothing but advance their Parinibanna.
We can break down acts and dissect motivations revealing that not all acts of a similar nature are the same. The manner in which karma accumulates is not, in my understanding, a mechanical ledger of "right" and "wrong".
I see the benefit of black and white morality in some contexts. I also see it as very problematic in others. On the other hand, relative morality is itself rife with problems.