Hackers are sophisticated nowadays. The DNC wasn’t that serious about security. It didn’t have to be an inside job.
Data rate supposedly indicates it happened inside
As Rush mentioned, the D/L speeds were too fast for net downloads...had to be onsite.
Certainly it’s possibly that their servers were hacked, but the metadata on the files that wikileaks received shows they were saved too quickly for them to have been transmitted over an internet connection.
For example, if you have a timestamp on file #1 that shows the copying was completed on 9:00:01 AM, and a timestamp on file #2 that shows the copying was completed on 9:00:05 AM, then you know that file #2 took 4 seconds to transfer, and if you divide the file size by 4 seconds, you will know how many megabytes per second the data was transferred at. If the rate is above a certain level, then you know it wasn’t transferred over the internet, it must have been a physical copy made through a direct connection.