ELLSWORTH — Serene and confident, a Blue Hill baby sitter accused in a “shaken baby syndrome” case took the witness stand in her own defense Thursday after a Hancock County Superior Court justice dismissed two of the state’s three aggravated assault charges against her.

Steven Juskewitch, deputy district attorney, and Anthony J. Giunta, defense counsel for Sally E. Ryan, 32, concluded the evidentiary portion of the four-day jury trial Thursday. Both are scheduled to present closing arguments Friday morning before Justice Margaret J. Kravchuk.

Ryan was indicted on three counts of aggravated assault against 3-month-old Matthew Russell in incidents alleged to have taken place at the sitter’s home on Feb. 27, March 6 and March 13, 1991. Regularly caring for Matthew on Tuesdays and Wednesdays, Ryan testified Thursday that she quit her $60-a-day job at a grocery store to become a $20-a-day sitter because she “thought it would be a good change.”

Her former employers, Leonard and Kim Russell of Ellsworth, were Ryan’s next-door neighbors at the time the child-care arrangements were made. Besides the criminal penalties sought against Ryan, the Russells also have filed a $2 million civil suit against the sitter, claiming their child exhibited signs of distress on returning from the baby sitter’s house on the three dates listed in the indictment.

Matthew, now 2 years old, is alleged to have sustained injuries described by four medical experts testifying for the state as consistent with shaken baby syndrome. Profound brain damage has left the Blue Hill boy retarded, blind, having cerebral palsy and with no hope of ever being able to walk.

At the close of the state’s case Thursday, Justice Kravchuk granted two-thirds of a motion for acquittal sought by Giunta, who said that the state had failed to submit sufficient evidence to support its allegations against his client.

Justice Kravchuk agreed there was a lack of medical evidence to substantiate the timing associated with the crimes as described in the doctors’ testimony, and dismissed the Feb. 27 and March 6 aggravated assault charges.

Juskewitch has built the state’s case on the findings of four Eastern Maine Medical Center specialists who treated Matthew and testified that shaken baby syndrome was the only logical explanation for the child’s injuries.

The infant’s parents claimed they noticed significant changes in Matthew’s behavior on picking up the child at Ryan’s. Accepting a Blue Hill doctor’s opinion that the baby’s general lethargy and loss of appetite were attributable to the flu, the Russells were forced to rush their son to EMMC on March 13 after he began to experience seizures.

Contrary to testimony provided by the Russells, Ryan said that Matthew was basically a happy and healthy infant who rarely cried or experienced difficulties. With the exception of a couple of incidents, the sitter said, she noticed nothing unusual in Matthew’s behavior.

She did recall a few times when the baby vomited his formula and the aftermath of a March 13 trip to Ellsworth during which he had his picture taken. After bringing the baby back to her home for a nap, Ryan said, she heard Matthew moaning and grabbing the sheets as if he were having “a bad dream.”

Kimberly Russell picked up her son at 5:30 p.m. and watched in horror as the baby went into a seizure a few hours later.

“Is there anything you can think of that you might have done to hurt or injure Matthew?” Giunta asked his client.

“No,” Ryan said.