Thompson said he prescribed more drugs than usual to MacNeill at the request of her husband. He said he felt comfortable doing so "because Martin was a physician and he asked me for these things."
A jury of eight people will decide the doctor's fate in a trial that is expected to last five weeks and pit MacNeill against his daughters, who are expected to be star witnesses for the prosecution.
One of them is Ada MacNeill, now 12 years old. Two of MacNeill's other daughters, Alexis Somers and Rachel MacNeill, are also expected to take the stand. Both have consistently been a presence in the courtroom during pre-trial hearings, often clutching pictures of their mother as they glared at their father.
The jury is also expected to hear from MacNeill's alleged mistress, who moved into the family's home as a nanny weeks after Michele MacNeill's death.