The man accused of carrying out a triple slaying at a Starbucks coffee shop in the District was in court yesterday trying to prevent prosecutors from using their most powerful evidence against him: statements in which he admitted opening fire on the victims.

Carl Derek Cooper, who made the incriminating statements in March during four days of interrogation by authorities, now contends that he lied under extreme pressure. An FBI agent testified yesterday that Cooper eventually disavowed the admissions and that Cooper said, "I swear on my father's grave and my son's life that I didn't do Starbucks."

Cooper, 30, is scheduled to stand trial April 10 in U.S. District Court in Washington on racketeering, murder and other charges. Prosecutors have not decided whether to seek the death penalty against him in a series of crimes that included the July 1997 killings at a Starbucks coffee shop at 1810 Wisconsin Ave. NW. But they cited a number of reasons to do so, including the cruelty of the attack on Starbucks employees Mary Caitrin Mahoney, 25, Emory Allen Evans, 25, and Aaron David Goodrich, 18.

Although D.C. law does not provide for the death penalty, some federal crimes can be punishable by death. The last execution carried out in the District was in 1957.

Cooper was arrested in March after an investigation by the FBI, D.C. police, Prince George's County police and other agencies. Authorities began looking at Cooper two months after the killings after getting an anonymous tip. They interviewed scores of associates, later wiretapped his telephone calls and even mounted a camera on a utility pole outside his home in the 1200 block of Gallatin Street NE.

While pursuing the Starbucks investigation, prosecutors said, the police-FBI task force tied Cooper to other crimes, including the shooting of off-duty Prince George's police officer Bruce Howard during a robbery attempt at a Hyattsville park in August 1996. When Cooper was taken into custody, he was charged in only that case.

Cooper's attorneys, Steven R. Kiersh and Francis D. Carter, argued that prosecutors built the Starbucks case on tainted admissions. Cooper now maintains that he told police what they wanted him to say. The defense wants Senior U.S. District Judge Joyce Hens Green to prevent prosecutors from using Cooper's statements at trial.

Assistant U.S. Attorney Kenneth L. Wainstein countered that the statements were made voluntarily and should be admitted as evidence.

FBI agent Bradley J. Garrett, who questioned Cooper about the Starbucks slayings soon after Cooper's March 1 arrest, quoted him as saying, "Killing someone is not my style" and said the denials continued for more than six hours, ending the first interrogation. Garrett said that when he next questioned Cooper, the suspect disavowed incriminating statements he had given to Prince George's police.

Defense attorneys argued that the Starbucks questions should have come to a halt after the first FBI interrogation. On March 2, Cooper appeared in D.C. Superior Court and waived extradition to Prince George's County for trial on the charge involving the off-duty officer's shooting. A public defender declared in court that day that Cooper would no longer speak with law enforcement authorities without an attorney, demanding the questioning stop.

But later that day, after arriving at Prince George's police headquarters, Cooper began making statements. Richard Fulginiti, a Prince George's detective, said Cooper repeatedly offered to provide information even though he was told he could have a lawyer.

During a 54-hour period, Cooper gave seven written statements to Prince George's police detectives, including three about the Starbucks slayings. He initially suggested an acquaintance had done the killings, then shifted stories, prosecutors said. Cooper later said he was a lookout for yet another man. But after police questioned that person, Cooper said he acted on his own in a robbery, prosecutors said, willingly offering details that were consistent with evidence found at the crime scene.