A 15-year-old boy charged Wednesday with killing another 15-year-old boy told police "I just blacked out. ... Then I unzipped my shirt, and I pulled out a gun and I just shot him."

St. Paul police confirmed Wednesday that William H. Grigsby Jr. is accused in the death late Saturday of Joshua A. Wilson-Shaw. Grigsby was charged in Ramsey County juvenile court with one count of second-degree murder. Prosecutors are seeking to have him stand trial as an adult.

According to court documents, Wilson-Shaw was in the back yard of a house in the 700 block of Case Avenue in St. Paul when he was approached by Grigsby, who tried to shake hands. It was "a gesture made because the two had previously fought," the juvenile petition said.

When Wilson-Shaw refused the handshake, Grigsby "felt dissed and became angry," the petition said. He pulled a gun from his waistband and shot Wilson-Shaw.

Police briefly interviewed Grigsby on Tuesday and he told them he fired six shots, then ran.

According to a search warrant affidavit filed Wednesday, investigators found .44- and .40-caliber bullet cartridges at Grigsby's home, which were consistent with the bullet fragments taken from Wilson-Shaw's body.

A 14-year-old boy and an man also were arrested in connection with the shooting. They will not be charged, the county attorney's office said.