Dan O'Meara:
As promised, I did the best I could in terms of answering the points you made in the OP over the weekend, and hope my answers are of some help to you in resolving your queries.
Before I go any further, I'd offer a few preliminary observations to give the matter some context:
(1) The dispatcher was not required to note the time after every transmission – it would have been very useful to us, but it didn’t happen in quite a number cases, particularly when there was heavy radio traffic
(2) Using transcripts alone to determine when things happened is fraught with danger. I did some study many years ago on the number of actual radio transmissions on the recordings, compared with those transcribed on probably the best publicly-available “verbatim” transcript of channel 1, and while I cannot now recall the details, I do remember that the transcript was woefully incomplete. While others may disagree, I honestly believe that listening to the actual recordings is the only way to get an accurate picture of what was going on, and how the messages between the dispatchers and the officers on the ground relate to one another in context.
(3) It is worth remembering that both DPD radio channels were voice-activated, so the recording devices did not record continuously
Now, to deal with the "5-8 minute" gap, and the “nine minute section of radio silence on Channel 2” mentioned in the OP, I have listened to the most complete copy of the DPD radio recordings that I have (which were obtained from NARA some years ago), and I have found the following:
The two radio channels were in sync at 12:45, when the “Attention all squads, attention all squads. The suspect in the shooting at Elm and Houston …” notification was broadcast simultaneously on both channels.
On Channel 1, the Dispatcher (Hulse or Jackson) tells 241 (Officer Hollingsworth) to collect some blood from the Blood Bank on Commerce Street and take it to Parkland Hospital. 241 apparently responds immediately, telling the dispatcher that he is “en route”. 18 transmissions/exchanges later, the dispatcher announces the time as 1:04 – this puts the call probably somewhere between 1:03 and 1:04, probably closer to the latter. Seven radio exchanges later, 241 reports that he is at the Blood Bank, and 6 transmissions later, Captain Souter advises the dispatcher that “241’s got it and gone” – namely, he has collected the blood, and has headed for Parkland.
Meanwhile, on Channel 2, the request from Patrolman Chism for a squad to go to the Blood Bank and pick up some blood and take it to Parkland occurs three transmissions after the dispatcher (Henslee) announced the time as being 1 PM, and before he announced the time as 1:03.
It was also noted in the OP that immediately after the “Blood Bank” message on Channel 2, Captain Souter asked for a status report on the well-being of the President and Governor Connolly. My interpretation of the recordings shows that the reply to Capt. Souter followed in the very next transmission, and also occurred before the time announcement of 1:03 on Channel 2.
In summary, then, I don't find any evidence of an unexplainable gap in the recordings, or a nine minute period of radio silence, in the 1 PM to 1:05 PM time frame on either channel.
As previously noted, my time is at a premium right now, and much of my old research is locked away (for reasons of space, primarily), but I hope that what I've posted here is on some value/help to you in your work.
Chris Scally.