Last month, we were shocked by the news that The Walking Dead had lost another show runner.  This time it was Glen Mazarra, who guided the series in much of season two and all of the current season.

Speculation sprang up as to why the hit series might need a second show runner in under two years and a lot of speculation has centered on AMC and series creator Robert Kirkman.

According to the Hollywood Reporter, two of Mazarra’s colleagues from his time on the hit series The Shield quickly jumped to his defense.  Shawn Ryan and Kurt Sutter were quick to defend Mazarra and criticize AMC for  the latest show runner change.

In a video on his web site, Sutter (who is no stranger to calling out the critics and network execs who question his own series Sons of Anarchy)  denounced AMC for departing from a cable culture that generally allows showrunners more creative freedom than do the broadcast networks. Kirkman, he added, “is an amazing visual artist and a graphic artist [but] knows very little about TV, and the reins keep going back to him in this process, and he doesn’t know how to run a show.”

Several insiders confirm that Kirkman, whose detailed graphic novels form the basis of the series, is “very proprietary,” as one puts it. One adds, “I believe Robert wants to maintain a certain amount of his control, and AMC needs Robert for the fan base.” But despite the vitriol, some sources involved with Walking Dead say Kirkman was one of several producers on the show who had issues with Mazzara and his vision.

One source says Mazzara’s shortcomings in running the series during the most recent third season became “abundantly clear … especially for the second half of the season.” This source says production was shut down “several times” because of a lack of material.

Mazzara declined comment but will participate in a Jan. 11 AFI awards luncheon that will honor Walking Dead as one of 2012’s top shows.