Cite as: 507 U. S. 272 (1993)
Per Curiam
dence of a prior criminal record." 890 F. 2d, at 722. Accord, May v. Collins, 904 F. 2d 228, 232 (CA5 1990), cert. denied, 498 U. S. 1055 (1991).
In short, until the Court of Appeals' decision in this case, it appears that lower courts consistently applied the principles established by Lockett and its progeny. Today we make explicit the clear implication of our precedents: Nothing in the Constitution obligates state courts to give mitigating circumstance instructions when no evidence is offered to support them. Because the jury heard no evidence concerning Lashley's prior criminal history, the trial judge did not err in refusing to give the requested instruction.
We are not persuaded by the Court of Appeals' assertion that the State was uniquely situated to prove whether or not Lashley had a significant prior criminal history. As an initial matter, Missouri law does not demand proof that a mitigating circumstance exists; it requires only some supporting evidence. Lashley acknowledged in his federal habeas petition that his attorneys could have put forward some evidence that he lacked a significant prior criminal history; indeed, he contended that they were constitutionally ineffective for failing to do so. App. to Pet. for Cert. A-71. There is no reason to suppose, as the dissent suggests, post, at 288, that Lashley would be required to testify in order to receive the mitigating instruction. Before the state trial court, the prosecution submitted that testimony by Lashley's acquaintances would suffice. App. to Pet. for Cert. A-83. On these facts, we cannot say that the State unfairly required Lashley to prove a negative.
Nor are we convinced that, as a general rule, States are better positioned than criminal defendants to adduce evidence of the defendants' own criminal history. While the prosecution may have ready access to records of crimes committed within its own jurisdiction, the same may not be true when the defendant has committed crimes in other jurisdictions, perhaps over a period of many years. And any pre-
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