Can a jury consider mitigating factors in their deliberations?

The defense requested a special instruction that would have told the jury: "A mitigating circumstance need not be proved beyond a reasonable doubt to exist." Although the prosecution did not object, the trial court declined to give the requested instruction, reasoning it could be misinterpreted to require all aggravating circumstances to be proven beyond a reasonable doubt, when some (for example, the defendant's age) need not meet such a standard. The trial court instead instructed the jury: "You may also consider, take into account, and be guided by the following factors in mitigation if you find them to be true...." and proceeded to enumerate various factors. Defendant contends the trial court erred in refusing his requested instruction and in failing sua sponte to give an accurate instruction on the burden of proof or persuasion as to mitigating circumstances, which would have entailed instructing the jury as to the substantial evidence standard (see People v. Wharton (1991) 53 Cal.3d 522, 600-601, 280 Cal. Rptr. 631, 809 P.2d 290).

We rejected a similar contention in People v. Welch (1999) 20 Cal.4th 701, 767, 85 Cal.Rptr.2d 203, 976 P.2d 754, finding no reason to believe that a jury, given instructions that aggravating factors must be proven beyond a reasonable doubt, but told nothing about mitigating factors, would think it could consider mitigating circumstances only if proven beyond a reasonable doubt. Likewise, we find no reason on the record of this case to believe the jury misunderstood its ability to consider mitigating evidence.