Nearly five hours after Prince George's County police arrested her on suspicion of fatally shooting her on-again, off-again boyfriend in her Capitol Heights home last January, Abere Karibi-Ikiriko became emotional in a small interview room at police headquarters.

She sobbed and screamed as a police video camera recorded her, according to a description by a defense attorney who later saw the videotape. She began to collapse and was held up by a county homicide detective. Karibi-Ikiriko asked the detective: How could you live if you knew you killed somebody you loved?

The Prince George's jury that decided Karibi-Ikiriko's fate this month never saw any of it.

A judge threw out the entire interview because he determined that Cpl. Bernard Nelson Jr., an 11-year veteran of the homicide unit, violated a bedrock principle of the criminal justice system: a suspect's right to an attorney.

It was one of four videotaped statements that circuit or appellate judges have suppressed since June because they determined the Prince George's police obtained them improperly.

And it was the second time in four years that a judge has tossed out a defendant's statement because Nelson disregarded a suspect's request for an attorney. During that time, Nelson also obtained a confession from a teenager in a murder case that turned out to be false.

After viewing a portion of the videotape in Karibi-Ikiriko's case, Circuit Court Judge Richard H. Sothoron Jr. ruled that none of Karibi-Ikiriko's statements during her 41/2 hours in an interview room were admissible because she'd asked for an attorney four times, which made the statements involuntary.

Karibi-Ikiriko's attorney Debra A. Saltz, describing the tape in court, said she counted six requests for an attorney in five minutes.

According to Saltz, Nelson told Karibi-Ikiriko she could change her mind and talk to him after the first two times Karibi-Ikiriko asked for an attorney. Karibi-Ikiriko again asked for a lawyer, adding, "You understand, right?"

On Aug. 8, the jury acquitted Karibi-Ikiriko, 27, of first-degree murder, which carries a possible sentence of life in prison, and convicted her of second-degree murder, which carries a possible maximum punishment of 30 years. She is to be sentenced Sept. 9.

In a previous case, in July 2001, Nelson testified in a court hearing that he ignored repeated requests by defendant Michael Eugene Shipman to speak to a lawyer, continuing to question him in the hopes of obtaining a confession.

A Circuit Court judge ruled that the prosecution could use the statements Nelson obtained only if Shipman testified at his trial. He did not testify, and the trial ended in a hung jury. Shipman later pleaded guilty to the lesser charge of manslaughter.

Two weeks after he questioned Shipman in early August 2000, Nelson conducted another interrogation that became controversial.

On Aug. 24, 2000, Nelson obtained a false murder confession from a teenager. It was one of three false admissions to murder The Washington Post documented in a series of articles in 2001.

Nelson did not respond to a phone message seeking comment.

Barbara Hamm, a police spokeswoman, would not specifically address Nelson's conduct in the Karibi-Ikiriko case. In a written response to a series of questions, she said, "The prosecution determined that Ms. Ikiriko's statement was sufficiently voluntary and free of Constitutional defects that it sought to introduce it for admission as evidence. Corporal Nelson's performance in this case and others is subject to periodic critique by his supervisor and the Commander of the Criminal Investigations Division. This process should identify areas for enhanced training and continuing education for investigators."

In general, she wrote in the response, "The fact that a trial court suppressed a witness statement does not in itself mean that the interrogating detective engaged in wrongful conduct."

State's Attorney Glenn F. Ivey said a prosecutor is available to detectives around the clock if they are unsure about what they can do legally during an interrogation.

"Overall, I think the detectives are doing a good job," Ivey said, noting that 45 of 50 murder or manslaughter cases this year have ended with a conviction, sometimes on a lesser charge, or plea bargain.

A 1981 U.S. Supreme Court decision requires law enforcement officers to stop questioning a suspect the moment he or she asks for an attorney, several legal experts said. The concept has become part of popular culture, with television police dramas often showing scenes in which detectives stop questioning suspects the moment they "lawyer up."

"This isn't particularly complicated. I think most police agents know that when someone wants a lawyer, you cease all interrogation," said Washington lawyer Aitan Goelman, a former federal prosecutor who now represents white-collar defendants.

A suspect could change his mind and waive the right to an attorney, provided there's no prodding by an officer, Goelman said.

Defense attorneys said they were troubled that a veteran homicide detective would ignore a basic legal principle.

"I think the leadership of the police department tries to divorce itself from what is going on in interrogation rooms," said Joseph M. Niland, the chief public defender in Prince George's. "If the leadership cracked down on this, it would be stopped."

After the false murder confessions were documented, Prince George's police in 2003 began videotaping statements in homicides and other major cases.

State's attorney's officials have said the videotaping has helped refute some allegations of police misconduct.

But the videotaping also has verified overly aggressive interrogation procedures by detectives. In 2003, a Circuit Court judge threw out the videotaped statement of murder suspect Richard B. Gater because a detective threatened to have a police raid conducted on the home of the suspect's ailing mother.

The same judge threw out a videotaped statement by Gater's co-defendant because two other detectives continued to question the alleged accomplice after he had checked "no" on a form asking whether he agreed to waive his right to remain silent.

In a third 2003 case, a Circuit Court judge suppressed a videotaped statement by a carjacking suspect because a county police detective ignored the suspect's request for an attorney.

And in June 2003, the Maryland Court of Appeals threw out guilty verdicts in three Prince George's trials -- a murder case and two armed robberies -- because county police detectives violated rules against prolonged interrogations of suspects.

Nelson isn't the only homicide detective to have a videotaped statement thrown out in recent weeks.

On Aug. 2, Circuit Court Judge C. Philip Nichols Jr. did not allow a videotaped statement obtained by homicide Detective Gregory McDonald to be used.

About 11:45 a.m. Feb. 17, McDonald began interviewing Robert Lee Humphries III. Less than two hours earlier, Humphries, then 34, had forced his way into his wife's apartment in Glenarden and fatally stabbed her despite an attempt by a private security guard for the apartment complex to protect her, according to a police charging document.

Nichols suppressed the defendant's statement because Humphries told McDonald at the beginning of the interview that he had consumed 10 beers about an hour before the attack. A blood sample taken from Humphries that day showed no alcohol in his system. McDonald testified that Humphries did not appear to be under the influence.

Humphries's attorney, Assistant Public Defender Denton Lynch, argued that because of the 10 beers, his client was incapable of knowingly and willingly waiving his Miranda rights to remain silent and ask for an attorney.

"It would appear that, at least to me, there's evidence from a witness for the defendant that he had been drinking, there is a notation to the waiver [of rights] form that he had in fact been drinking, and I'm just not prepared to say that beyond a reasonable doubt his statement, what little there is, was given voluntarily," Nichols said, explaining why he suppressed the statement.

Humphries is scheduled to go on trial today.