Eric Knudsen basically caused a lot of fear in people and even caused people to kill them selfs and even other people!If he didn't create slender man in the first place then none of this would have happened and we already have enough murder and suicide in this messed up World.
The author isn't at all responsible because the description of the motive given by the girl do not match Slenderman's actions in fanfics he's in. He doesn't enlist people to be his proxies, he has no mansion where he lives, and he doesn't manipulate people to kill each other. These girls are obviously making all the stuff up or mre obviously, mentally unstable.
He just used his imagination to create a fictional character on the internet. It would be like blaming Rockstar games (creators of GTA) for when a car is stolen. I sincerely believe these girls had mental issues that hindered them from distinguishing fiction from reality. There are tons of 12 year olds that read these types of stories and don't attempt to murder people.
First of all, Slenderman is a made up character to further "spook" people out (mostly teenagers). It's like the boogeyman. He's not real, he's simply made up. Where were the parents of these 12 year old girls? They should be held responsible as they are the ones that take care of them, not Eric Knudsen.
Slenderman is nothing but a story, and urban legend. It's a creepypasta for Godsakes. Charging him with a crime would be like charging every violent video game creator for every time that there was a school shooting for indiating it. It would thus lead to a slippery slope of cracking down on video games as this would lead to internet censorship on these type of stories.
There have always been characters and stories like Slenderman and people have not used those stories as an excuse to hurt people in the past. Obviously these two young girls had a mental problem and unfortunately used slenderman as an outlet to fuel their illness. If it wasn't this horror fiction it would have certainly been another and unless we want to outlaw all scary stories, then we cannot blame the creator.
No, even though Eric Knudsen might has been cited in creating the ideology behind Slenderman, in no way did he directly instruct the 12 year-old girls to attempt murder. While it might be hard for people to believe girls so young would act in such heinous fashion at their own free will, I believe it is possible.
Eric Knudsen is an artist and was inspired by writer Stephen King. People with imagination should not be punished for the actions of others. Knudsen did nothing to encourage violence and it was never his intention for people to carry out attacks on other people. He did not expect the character to become widely known.
I do not think that Eric Knudsen can in any way be held responsible for the actions or arrest of these two 12 year-old girls. His writings are purely fiction, and not intended to influence peoples behaviour. If people decide to read too much into them, he cannot be held responsible for that.