Shirlita Colon hardly had a chance to show how good a parent she could be.

The 15-year-old was shot twice in the head last Mother's Day and left to die in an alley around the corner from her family's home in Southeast Washington. Shirley, as she was known to everyone, had been a mother for little more than a couple of months. As young as she was, family members said, she was determined to be a good mother to 10-week-old Destiny.

But the baby's father, Donte Allen, was anything but supportive. In opening statements at his trial in D.C. Superior Court yesterday, prosecutors described Allen as an angry teenager who saw his child as a burden he would have to bear once it became clear he was unable to deny that he was the father.

The anger turned deadly May 12, when, prosecutors say, Allen gunned down Colon after she asked him for money to buy diapers. Allen, who was 17 at the time of the shooting and is now 18, was charged as an adult with first-degree murder. He has pleaded not guilty.

Allen's attorney, Ronald Horton, said in his opening statement that the government had nothing more than a "theory" and a witness spouting self-serving "nonsense." Dressed in a sky-blue shirt and silver tie, Allen, of the 2700 block of Langston Place SE, showed no emotion as he listened to the first day of testimony in the third-floor courtroom of Judge Geoffrey M. Alprin.

First to take the stand was Colon's older sister, Tysha, who was home visiting last Mother's Day and had just left for Fairfax County when her sister was shot. Wearing a denim jacket with "Shirley 1986-2002" in glittery letters across the back, Tysha Colon testified that she saw her little sister and Allen arguing in the stairwell about an hour before the body was found. "I knew she was angry, because there were tears in her eyes," she said.

Afterward, she said that her sister, who was a student at Eastern Senior High School and wanted to design clothes for a living, wasn't the type to fight or argue. Until the argument with Allen, she had never seen her sister so angry.

"I know that it was him, because I've never seen her have a conflict like that with anyone," she said.

But it was Melvin Cuffe, a longtime friend of Allen's, who offered what may be the most damaging evidence. Cuffe testified that he was present when Allen pulled a gun on Shirlita and shot her twice in the head in an alley in the 800 block of Hilltop Terrace.

"He took a step out of the car and shot her," Cuffe said during questioning by Assistant U.S. Attorney S. Elisa Poteat.

In three hours of testimony, Cuffe provided his account of the minutes leading up to the teenager's slaying and of the events that followed. Cuffe said he did not know what the defendant planned when he stopped the car they were riding in to pick up his ex-girlfriend shortly before 9 p.m. as she waited at a bus stop near her family's apartment complex in the Benning Terrace neighborhood.

Only when Allen pulled into the alley off Hilltop Terrace and reached into his waistband to retrieve a small black pistol did Cuffe realize that there might be trouble, he testified.

Allen, Cuffe told the court, turned around and pointed the gun at Colon, who was in the backseat. "She was yelling, 'Stop playing,' " he said. Fearful, she jumped out of the car and tried to scale a fence, but her foot got caught and she couldn't escape, Cuffe said.

Allen, Cuffe testified, then shot her once in the head. When Cuffe asked his friend what he was doing and urged him to bring Colon to the hospital, Allen dismissed the idea and shot Colon a second time, Cuffe told the court.

When the two talked a couple of days later, Allen offered an explanation for the shooting: "I'm too young to be a father," Cuffe testified, quoting Allen.

Horton, the defense attorney for Allen, worked hard to punch holes in the credibility of Cuffe, who admitted lying to police initially to avoid incriminating himself.

Detectives had been tipped off that Cuffe was a close friend of Allen's and might have information on Colon's killing, and when they searched Cuffe's house, they found a gun and arrested him. Cuffe was charged with a misdemeanor count of gun possession that was later dropped.

Only after hours of questioning did Cuffe tell police that he had been in the car with Allen and that he had witnessed the shooting, he told the court yesterday under spirited questioning by Horton, who was trying to persuade the jury that the account Cuffe was giving the court might be a lie, too.

Cuffe, who expressed some frustration at Horton's fast-paced questioning, did his best to explain away his lies. "I just didn't want to be involved in what happened," he said. "I tried to make it seem like I wasn't there. The stuff I'm going through now, I didn't want to go through. I don't look for trouble. I don't start trouble."