There are two separate entities publishing documents about DNC emails. One is a blog by someone who calls himself Guccifer 2.0, the other is Wikileaks. The name Guccifer comes from a Romanian hacker who was extradited earlier this year to the US. An individual who claimed among other thing that they hacked Clinton's emails.
The problem is that the DNC information security was bad. Former NSA and CIA director Hayden said:
So, without concrete evidence, which I don’t have, and apparently the FBI doesn’t have either, what I have felt comfortable saying about this is that I would lose a whole lot of respect for a whole bunch of intelligence agencies around the world, if they hadn’t penetrated that server and gotten access to the emails.
That means that will Russia likely has hacked the DNC, so have a whole bunch of other intelligence agencies.
Any of those intelligence agencies, various private hackers and also various people inside the DNC could have given Wikileaks the data.
Two ex-NSA employees with Edward Snowden and William Binney said that the NSA has the capability to say if Russia is guilty.
At a time where the mainstream media found Russia guilty NSA chief Clapper said:
Director of National Intelligence James Clapper said today he’s “not ready” yet to say Russia was behind the DNC hack.
Does the information from Guccifer 2.0, the other is Wikileaks come from the same source? Guccifer 2.0 claims it does, Wikileaks doesn't confirm or deny but states there no public evidence that it comes from the source. Given that it's likely according to Hayden that multiple intelligence agencies have access to the information it's not impossible that the information comes from different sources.
Wikileaks itself publishes documents in a clean form. Some of the documents that Guccifer 2.0 gave to news outlets (not the files Wikileaks released) contained meta data that included Russian information. The Russian intelligence agencies are usually competent enough to not leave traces like that, so you could see this as evidence that one of the other intelligence agencies who after Hayden assessment also have access to the DNC information wanted to harm US Russian relationship.
Craig Murray who was a former ambassador of the United Kingdom said that he knows who the source of the documents that Wikileaks published happen to be and it isn't the Russians. He claimed that the documents came from leaks and not from hacks. According to him the source had legal access to the documents.
Julian Assange also said that Wikileaks didn't get the documents from a state actor.