I don't remember where I read the reason DHS got it, but what I read indicated that the homeowner told a trusted law enforcement officer about the video and their suspicion that it MAY be relevant to the investigation. The law enforcement guy was DHS, so he naturally had DHS retrieve it. I believe that the more recently acquired videos are with the FBI. The DHS will also send the homeowner video to the FBI. CNN ex-FBI guys are dismayed that the first video did not go directly to the FBI....but I think they may not have realized that the DHS handled it because the friend of the homeowner is DHS. JMO JMO JMO
But why would the DHS not take the video to the investigating agency? I've had to report things to my local LE when I couldn't get county to reply. fortunately I have a good enough relationship with our local LE that an LEO took my tip to county. I can understand a homeowner going through another agency, but not the other agency not going through the investigating agency.