The official line so far is "The DPRK is responsible, but the attack originated from somewhere else".
"Responsible" most likely means hired someone to do it. Knowing the DPRK they probably paid those someones in reasonably good quality counterfeit US currency. Though that is pure speculation on my part bast on past news events.
The fact they won't tell us form where else means "China" again pure speculation on my part but common its not like DPRK has exactly normal relations with anywhere else. They would tell us if it was some other pariah regime some place, so I assume it has to be China as its the only place I can think of that DPRK would have access and would be to politically sensitive to name.
Russia also fits the bill, although I'm not surprised that you didn't know that. Russia still has reasonably friendly relations with North Korea and shares a small border with it where North Korean "guest workers" (really slave labor) do logging and perhaps some other manual work on the Russian side for little pay and without any choice in the matter. Putin just recently said he was looking to improve relations between the two countries. North Korea spent years playing its patrons the Soviet Union and China off each other. The USSR and China had strained relations for many years and North Korea leaned towards whichever side at the time it could get more money out of. The Soviet Union gave them their first nuclear reactor and the training necessary that put them, if unintentionally, on the path to getting nuclear weapons. Boris Yeltsin had the good sense a long time ago to stop all payments to North Korea, basically saying "Too bad. So sad." They've never been resumed. So he left China holding the bag for being 100% responsible for financially propping up the regime. Kim Jong-Un's father was actually born in Russia, although official reports in North Korea deny this. And his grandfather was a Russian military officer during the 2nd World War and became the eventual dictator of North Korea because Russia's first choice for the job turned it down and grandpa Kim seemed loyal enough to the Soviet Union to be a really good back up choice. So while Russian-North Korean ties don't get much press, Russia gets all of the benefits, whatever they are, of being "friends" with North Korea without any of the costs that China got stuck with.