Dawn of the Dead (4/11) Movie CLIP - The Dead Will Walk the Earth (2004) HD
There's a backstory here on the first few seconds of the clip.
Watching the news ticker, it says: Secretary of Defense Wesley Coller has firmly denied that any part of the current is due to any chemical or biological attack. "Due to the number of friendly and unfriendly countries involved in the outbreak, we have no reason to suspect any terrorist involvement."
Since the movie is set in May 2004, the memories of 9/11 and the ongoing deployments in Afghanistan and Iraq are still fresh in people's minds. Hence, it would be natural to think that the zombie virus was a bioweapon.