ScotusBlog's sister blog, Supreme Court Nomination Blog, has these criminal law opinions written

Fourth Amendment
United States v. Lawson, 2005 U.S. App. LEXIS 10798 - Writing for a unanimous panel, Judge Roberts rejected numerous challenges to a conviction for bank robbery. In particular, he upheld the warrantless search of defendant's car. Judge Roberts found that the fact that the car matched an eyewitness description and that officers saw latex gloves on the front seat created probable cause for the search.

Criminal Sentencing
United States v. Mellen, 393 F.3d 175 (D.C. Cir. 2004) - Writing for the majority over a dissent by Judge Henderson, Judge Roberts found that the district court had erred in attributing to the defendant the value of all of the goods stolen by his wife and stored in their shared home. Judge Roberts held that mere knowledge was insufficient to render the defendant responsible for the goods. Instead, the government had to establish that he had agreed to participate in the conspiracy or taken affirmative steps to facilitate the crime.

Ineffective Assistance of Counsel
United States v. Toms, 396 F.3d 427 (D.C. Cir. 2005) - Writing for a unanimous panel, Judge Roberts rejected the defendant's claim that his lawyer failed to provide effective assistance because he failed to call a witness and stipulated to a conviction that had been expunged. Judge Roberts found that some aspects of the challenged conduct were strategic choices and therefore "virtually unchallengable," and that the erroneous stipulation was unreasonable but harmless.