The younger brother of a Salvadoran dishwasher testified yesterday in the trial of a Laurel teenager charged with murder that the fatal attack began as an armed robbery. And his account of a robbery was bolstered by another prosecution witness who said he overheard teenagers talk of robbing the brothers moments before the attack.

The testimony of both witnesses seemed to contradict prosecutors' version of the assault, for which they said there was no clear motive.

The testimony also raised questions anew about how Prince George's County State's Attorney Jack B. Johnson has handled prosecution of the teenagers who allegedly participated in the fatal attack on Gilberto Hernandez, 40, in September 1998.

Some advocates for Latinos and others have criticized Johnson for dismissing the possibility of a robbery and for not interviewing until seven months after the attack Juan Hernandez and another brother who was at the scene moments before the fatal assault.

They have also questioned why the three youths charged with killing Hernandez were charged with common-law murder rather than felony murder, which does not require the government to show premeditation. A first-degree murder conviction under the common-law count does require a showing of premeditation.

In his opening statement Monday, Assistant State's Attorney E. Wesley Adams told jurors there was no explanation for the assault on Gilberto Hernandez.

According to prosecutors, Cochise Iraun "Cody" Queen, 18, tackled Hernandez as the immigrant was running from others in the group. Queen, a former football star at Laurel High School, hit Hernandez so hard he knocked the man off his feet, Adams said in his opening statement. Hernandez's head slammed against the concrete with a thud, he added.

As Hernandez lay on the ground, another of the youths charged with murder, Kellie Day Martin, 19, kicked his head soccer-style, Adams said. The back of Hernandez's skull was cracked by hitting the concrete, and the right side of his head was fractured by the kick, Adams said. Adams told the jury that the teenagers had decided to "mess with" Gilberto, Juan and Tomas Hernandez, 26, as the three brothers made their way home after work at a Chinese restaurant.

Despite the surviving brothers' statements to Laurel police, who conducted the original investigation of Hernandez's death, prosecutors did not interview the men until April, five months after charges were dismissed against four of the seven youths originally charged with robbing and killing Hernandez.

After the Hernandez brothers finally were interviewed, assault charges were added to the murder charges against Queen, Martin and Steven Darby, 17.

Under questioning by Assistant State's Attorney Fran Longwell, Juan Hernandez, 22, testified yesterday in Queen's murder trial that as he and Gilberto walked home from their restaurant jobs just before midnight Sept. 4, 1998, a group of youths asked them for money. As the brothers kept walking, the teenagers asked again, in an "angry and aggressive" manner, and he and Gilberto walked faster, Juan Hernandez testified. One of the teenagers brandished a knife, and he and Gilberto ran in different directions, Juan testified.

A second prosecution witness, Mark Ramsay, testified that he was with Queen's group moments before the assault began and heard Martin suggest a robbery.

Ramsay, dressed in his Air Force uniform, testified that he was with a group of teenagers and young men who were hanging out in a parking lot when Tomas Hernandez rode by on his bicycle.

Martin said the bike was his, and he and other members of the group ran after Tomas but returned without the bike, Ramsay testified.

Shortly after that, as Gilberto and Juan Hernandez walked by, Ramsay testified, he heard Martin ask whether the members of the group wanted to rob them. Ramsay testified that he said no but that Martin and several others ran after the brothers.

In other testimony yesterday, defense attorneys hammered during cross-examination at the credibility of the four against whom charges were dropped in exchange for their testimony.

Gerald Culbreath, 16, testified that he saw Queen slam into Hernandez and heard Darby cry out "Goldberg," a term named after a wrestler who tackles opponents. But under cross-examination by defense attorney Paul S. Christian, Culbreath said he had lied to Laurel police when he told them another teenager who wasn't involved in the attack had kicked Hernandez.

David Eugene Burley Jr., 20, who also obtained immunity for his testimony, testified that he saw Queen hit Hernandez "like a linebacker." Under cross-examination from Christian, Burley said he had lied to the grand jury when he blamed the attack on a teenager who didn't participate in the attack.

Prosecutors rested their case yesterday after Jacqueline Lee of the D.C. medical examiner's office testified about Hernandez's wounds. The defense is scheduled to present its case today.