If god gave humans free will, and that free will allows evil, then in some ways god can be blamed for causing evil.
*poorly written metaphor time*
Giving someone a gun doesn't necessarily create a "malevolent" situation, but giving a gun to someone who you know will use it to cause harm would make you "malevolent".
And if god is omnipotent, then he would therefore know who will and who won't use free will for evil and chooses to give free will to someone despite knowing how they'll use it. It's like giving a criminal a gun knowing full well that they're going to use it to knock over a nearby bank, likely killing a couple people in the process.