The 911 call came in early on the morning of Feb. 1, a Sunday. A 10-month-old girl was in trouble in the 1600 block of Sixth Street NW. Off went the D.C. Fire Department -- Engine No. 6 and Ambulance No. 6 -- to the three-story brick building at Sixth and Q, the one with the fresh coat of red paint and the front door that sticks open. The police showed up, too, at 7:43 a.m.

Here is what you'd expect a baby to be up to at 10 months: She should be crawling with great confidence now, maybe even standing up while hanging on to the furniture -- and exploring like mad. She should be starting to pick up small objects with her fingers. She should be talking gibberish and saying "Mama" now and then.

Here is what the cops and firefighters found: an unconscious baby, on whom they performed CPR on the way to Children's Hospital but who was pronounced dead at 8:03 a.m. The cause of death was methadone poisoning. The baby's 38-year-old mother had been using the synthetic drug to wean herself from heroin.

Tracey Lynn Cobb told police she had used a medicine dropper to add methadone to her daughter's formula two or three times a week over eight or nine months. She did this because her daughter was "a sick baby," she said. On Jan. 31, she had given her a larger dose than usual.

Cobb has been charged with first-degree felony murder.

She felt "so sorry" for her baby, the police reported.

She had called her Symphony -- a beautiful name, a hope for harmony.

-- Bob Thompson