When I first read the article headlined "Police Officer Will Not Be Charged For Killing Napster Exec While Texting And Driving — Because It's Apparently OK For Police To Do That" I expected it would be a somewhat cynical view discussing how police are above the law in practice, etc.
However, when reading the official document where this result was determined, I saw the explicit carve-out cited, from CA Vehicle Code 23123.5, CA's law against texting while driving. Section (e):
This section does not apply to an emergency services professional using an electronic wireless communications device while operating an authorized emergency vehicle, as defined in Section 165, in the course and scope of his or her duties.
Since this texting-while-driving death was caused by a deputy officer in the performance of his official duties, it falls under this exception and makes what the officer did legal. Why was this exemption specifically written in to the law? Why did the legislature choose to make it legal for an officer to text while driving, even if that kills somebody, while that's prohibited for others?
This law was added in 2007-2008 SB28 Sec. 2. (Parts of it other than (e) were amended in 2011-2012 AB1536 Sec. 1.) The bill that added the law can be found here. The votes are listed here, indicating passage by a pretty good sized majority.
The bill digest does not mention the exemption for emergency services professionals, nor does the fact sheet or letter to the Governor available from the sponsor's web page for the bill. Summaries in analyses of the bill do list the exclusion but don't explain why or where it comes from, other than indicating there's also an exemption in previously existing law regarding voice calls. (Note: "08/01/08- Senate Floor Analyses" appears to be about Senate Joint Resolution 28 rather than Senate Bill 28; 07/06/07 and earlier analyses seems to be about RFID licenses instead).
I found an additional bill history system here but it doesn't seem to add new information. I could not find debate records that might explain why this exclusion is in there which might help answer the question, but I hope I've demonstrated sufficient research here for it to be a good asking of the question.
If the same exception exists in another jurisdiction and you're able to explain why it exists for that one instead, that's still a welcome answer (please just be clear about the jurisdiction).