More than three decades after the death of his 5-year-old brother, a man told police he thought his mother was to blame. After a case review, she was arrested in Florida on a charge of first-degree murder.

Diane B. Coffman (search), 57, plans to plead innocent, defense attorney Domenic Iamele said Friday.

"She's aghast," Iamele said. "She was living a normal life, and all of a sudden the police come and charge her for the murder of her child. ... This comes completely out of left field."

The Baltimore County (search) investigation into the 1972 death of Edward Coffman (search) had been dormant until July, when deputies received the tip from Richard Coffman, who was 3 when his brother died. The e-mail discussed his mother's character and things that happened after the death, department spokesman Bill Toohey told The Washington Post.

During the original investigation, the mother told police she found her son Edward dead in his bed, hours after he had fallen in a tub at their Woodlawn home.

The autopsy showed 17 injuries, some suffered earlier. Police now say the injuries were inconsistent with the mother's story, and the medical examiner last month changed the manner of death from undetermined to homicide.

Dr. David Fowler, the state's chief medical examiner, said "a greater understanding of the mechanics of injuries played a part in the revision."

Coffman was arrested Tuesday at the dental office where she worked in Orange City, Fla., and returned to Baltimore County.

Bail was set Friday at $25,000. Her attorney said she will post bond and then return to her home to DeLand, Fla., where she moved in 1999.

Police declined to identify the hometown of Richard Coffman, now 35. Iamele described him as a "disgruntled child," saying he has been angry at his mother since he was 10. The attorney hadn't seen the e-mail. "We all want to look at that e-mail," he said.

The suspect's brother Gene Kelso, who appeared at Friday's hearing, said only that the family was surprised by the arrest. "This is all still new," he said. "I want to see what's going on."

Christine Shouse, who lives near Coffman and her husband, said the couple often looked after their young grandson.

"I hope everything works out for her, because they take such good care of that grandbaby," she told The [Baltimore] Sun.