The trial of a man charged with killing his ex-girlfriend ended in a mistrial Friday after a D.C. Superior Court jury failed to reach a verdict on the most serious charges following two weeks of arguments, testimony and deliberations.

Prosecutors alleged that Robert Ridley kicked in the door of his ex-girlfriend’s Southeast Washington apartment and stabbed her to death Nov. 21, 2008. Ridley, 34, was charged with 30 counts in the death of Tiffany Gates, 33, including first-degree murder, theft, threats, conspiracy and burglary.

The jury convicted Ridley earlier this week of 25 counts, including burglary, making threats and obstruction of justice, and cleared him on another threat charge. On Friday, they found him guilty of carrying a dangerous weapon.

But the jurors remained deadlocked on three murder charges, and Judge Gerald I. Fisher declared a mistrial late Friday afternoon. The prosecution has until July 28, when Ridley is scheduled to be sentenced on the other counts, to decide whether to retry him on the murder charges.

Prosecutors in the case declined to comment Friday.

According to testimony, Gates called police and a U.S. marshal for help after seeing Ridley outside her home. The marshal was on the phone with her, awaiting backup in a parking lot outside her apartment building, when he heard her scream, “He’s kicking down my door!”

When the marshal and a police officer got inside the building and up three flights of stairs seven minutes later, Gates was found bleeding in the hallway. Police later found the 6-foot-4 Ridley hiding under the sink of a vacant apartment, according to testimony.

But there were no witnesses, and no DNA evidence linked Ridley to the killing. Ridley was found with two stab wounds on his arm, and while Gates’s DNA was found on his bloody sweat shirt at the time of his arrest, so was that of a third person who was never identified.

“In this day of increasing questions of forensic evidence, it’s appropriately right not to convict when there are unanswered questions that should have been answered by the government,” said Cary Clennon, Ridley’s attorney.

Tension in the jury room was evident during the trial. In one note from the jury to Fisher this week, the forewoman wrote that their “failure to come to an agreement” was due to a “strong hesitance to [find] the defendant guilty on charges that will negatively affect him.”

The forewoman also suggested tension among jurors who disagreed with one another’s thought processes as they deliberated. “There seems to be more scrutiny in the lack of evidence (why didn’t prosecutor do this and why didn’t prosecutor do that) than the evidence that was presented,” the forewoman wrote.

Perhaps most striking, however, was a note from the forewoman in which she wrote that “one or more” of the jurors had a “bias” against the police department. “This main fact will prevent us from coming to a unanimous decision,” she wrote.

Fisher asked several jurors about the alleged bias during a bench conference but determined that no such bias existed.