A D.C. Superior Court jury convicted a Southeast Washington man yesterday of the 1978 slayings of his two aunts and an uncle. The conviction came a day after he testified that he had killed them because of childhood memories of their unkind treatment of his grandmother.

Melvin Jones, 29, of 123 I St. SE, was convicted of 13 out of 16 counts of murder, armed robbery and first degree burglary. He was acquitted on two counts of felony murder and one count of first degree murder.

Jones shocked his attorney, Grandison Hill, and sent gasps of surprise through the crowded courtroom Wednesday when he took the witness stand and quitely told how he carried out a childhood vow to kill his uncle, John Covington, 68, and Covington's wife, Virdell, 60, for mistreating Jone's grandmother years before.

"First I stabbed her," Jones said in the description of his aunt's slaying. "I stabbed her and then I shot her. All at the same time."

Jones told the jury that with a friend, Andre Jones, holding the victim on the floor, Melvin Jones stabbed his uncle 44 times. Andre Jones, no relation to Melvin Jones, was convicted in February of three counts of felony murder in the slayings.

Assistant U.S. Attorney William O'Malley contended in the government's case that Jones went to his uncle's home to commit robbery. O'Malley maintained that John Convington was widely known as a "numbers man," and kept large sums of cash in his home.

Jones, who also convicted yesterday of the stabbing death of his deaf aunt, Carolyn Bruton, 64, left fingerprints in two locations at the scene, according to government witnesses. A palm print in blood was left on a steak knife in the stabbing, according to testimony.

The bodies were found in their home at 3028 P St. SE on the afternoon of Sept. 28, 1978.

The night before the slayings, Jones testified, he bought a .38-caliber pistol. He also said four knives were used in the stabbings.

Jones told the jury that his uncle made Jones' grandmother live in the cold basement of their P Street home. As a young child, Jones -- who lived with his grandmother -- testified he was helpless to do anything about her mistreatment. But Jones testified he would eventually kill his aunt and uncle.