What percentage of all first-degree murders in the U.S. [or even in
one state, such as California, if these data are easier to find]
result in a capital sentence at trial? PRoblem: Given the length of
time it takes for some crimes to come to trial and get a sentence,
there may not be any one-to-one correlations possible. It may be
easier to answer: What are the odds of committing aggravated murder
and being executed? Info needed for a book on the death penalty.

Hello.

About 1.4% of murders in the U.S. result in death sentences.

"In the last quarter of a century, almost 500,000 murders have been
committed in the United States. Slightly more than 7,000 of the
murderers received death sentences and fewer than 800 have been
executed. The death penalty is properly reserved for the worst of the
worst."
source:
'All myths aside, Death Row is not filled with innocents'
By Joshua Marquis
Special to the Los Angeles Times
http://polkonline.com/stories/030102/opi_death.shtml

"In 1999 the number of persons executed in the United States increased
by 45 percent. This figure is puzzling when it is coupled with the
fact that the number of homicides has decreased from 20,000 to 16,000
a year. Of these 16,000 homicides approximately 280 get the death
penalty each year.
In other words, only 1 to 2 percent of those who commit murder get the
death sentence in this country."
source: Socialist Action
http://www.socialistaction.org/news/200105/death.html

--------

Similarly in California, less than 2% of murderers receive a death
sentence.

"California's death penalty law targets only the worst murderers and
district attorneys rarely seek the death penalty for qualifying cases.
Less than 2% of all murderers in California were sentenced to death in
2001."
source: California Office of the Attorney General
http://caag.state.ca.us/newsalerts/2003/03-034.htm

"In 2001, we had just over 2,200 murders in California. A mere 25
convicted murderers -- about 1 percent -- were sent to death row."
source: "NO: Death penalty assures final justice in our worst crimes"
Mercury News
http://www.siliconvalley.com/mld/mercurynews/news/opinion/6070452.htm

More statistics available in:

Death Penalty Sentences in California 2001
http://caag.state.ca.us/cjsc/publications/homicide/hm01/dp.pdf
Homicide in California (2001)
http://caag.state.ca.us/cjsc/publications/homicide/hm01/cr1.pdf
Homicide in California, Part 2 (2001)
http://caag.state.ca.us/cjsc/publications/homicide/hm01/cr2.pdf 
"PERSONS UNDER CALIFORNIA SENTENCE OF DEATH, 1978-2001"
http://caag.state.ca.us/cjsc/publications/homicide/hm01/tabs/hm0135.pdf


search strategy:
california, percent, "death sentence"
california, murders, percent, "death penalty"

I hope this helps. If anything is unclear or requires amplification,
please use the "request clarification" feature. Thank you.

This is just the info I needed.  The hard data is hard to come by, but
at least I can give an estimate range that many seem to agree upon. 
Thank you.

I didn’t find hard statistics to support a particular percentage, per
se, but I did find these notations if you’d like to accept these as an
answer:

“Less than one percent of all murder convictions result in the death
penalty…”
THE DEATH PENALTY
http://www.geocities.com/Athens/Forum/8512/death.html

“…only a small percentage of murder cases result in the death
penalty…”
A MORATORIUM ON DEATH: A PARADIGM FOR PENNSYLVANIA
By Jack L. Gruenstein
http://www.vairariley.com/AuNewsDetails.asp?NewsID=16

I don't know that hard factual statistics are available that would go
undisputed (I am actually in law enforcement myself and still couldn't
seem to find any hard data). There seems to be a great deal of
sentencing disparity between races, genders and regions (ranging from
states all the way down to municipal jurisdictions) that would likley
render any figures mere estimates at best. Even still, it would make a
difference if the person was convicted of a Federal crime or not,
since Federally imposed executions are even more rare.

Please let me know if this suffices as an answer.

Regards;
Tutuzdad-ga