GRUNDY CENTER - The prosecution has rested its case in the murder trial of Michelle Kehoe.

Kehoe is accused of killing her 2-year-old son, Seth, with a knife and wounding her older son, Sean. That happened just over a year ago in rural Buchanan County.

Prosecutors called only a single witness before resting Tuesday morning, Deputy Iowa medical examiner Dr. Dennis Klein, who autopsied the body of Seth Kehoe.

Dr. Klein ruled that the child died from a critical loss of blood. The knife wound did not sever an artery but instead cut a vein in the neck. The medical examiner says that likely would have meant the child was conscious for at least a few minutes before loss of blood rendered him unconscious.

The defense made a motion for a directed verdict of acquittal but that was quickly overruled.

In a delayed opening statement, the defense admitted Kehoe killed her young son, Seth, and tried to kill older son, Sean. But defense lawyer Andrea Dryer said what happened in October 2008 was the end result of a long struggle with mental illness.

Dr. William Logan, defense psychiatrist, told jurors Kehoe's medical history contained at least two documented serious attempts at suicide. The defense expert says Kehoe received both drugs as treatment over the years and at least 44 instances of electro-shock therapy.

Logan says that a traumatic event in December of 2007 may have led to subsequent events. Kehoe, with her two sons in the car, drove off a road and into the Iowa River in Iowa City. Everybody was rescued and the incident was treated as an accident at the time.

"There is some debate about if that was a suicide attempt or whether that was an accident - she has made statements both ways," Dr. Logan said.

Dr. Logan says regardless, that event triggered more suicidal thinking and perhaps led up to what happened in October 2008 in Buchanan County.

"Kehoe believed maybe her kids would be better off dead because their lives would be horrible. She didn't want them to face mental illness like she did," Dr. Logan said.

The defense expert concluded that the rational part of Kehoe's brain had lost contact with reality and that would meet Iowa's definition of insanity.