AUBURN – A Lisbon woman’s retrial for manslaughter ended Friday when jurors found her guilty of causing the death of her 21-month-old son.

The Androscoggin County Superior Court jury returned the verdict against Sarah Allen, 31, after 13 hours of deliberations over three days. Allen’s first trial last June ended in a mistrial when jurors failed to agree on a verdict.

Allen remained free after the verdict, and Superior Court Justice Ellen Gorman set no date for sentencing. Manslaughter is punishable by up to 40 years in prison.

Allen was accused of shaking her adopted son, Nathaniel, to death. She called 911 on Valentine’s Day night two years ago after noting that the toddler was unconscious. He died a couple of days later.

The prosecution said Allen caused the boy’s head and neck injuries. But an expert witness for the defense maintained that the youngster suffered developmental delays and showed signs of having a pre-existing brain disorder.

Jurors began deliberations late Wednesday after closing arguments. On Thursday the panel asked to see videotapes and audiotapes of Allen’s police questioning and also asked to review transcripts of testimony from several of the state’s medical experts.

Interviews with jurors after the first trial indicated that the panel was divided 11-1 in favor of conviction, with the lone holdout holding firm to her belief that the defense raised reasonable doubt about Allen’s guilt.

Allen’s husband, Jeremy Allen, was convicted last September of an unrelated assault against Nathaniel the day before he died.