JOLIET, Ill. (CBS) — A defense witness at the murder trial of Christopher Vaughn doesn’t appear to have helped his case.

As WBBM Newsradio’s Nick Young reports, attorneys for the Oswego man maintain it was Vaughn’s distraught wife who murdered her three children, shot him and then killed herself in 2007 when the family sport-utility vehicle was pulled over on a frontage road near Channahon.

LISTEN: WBBM Newsradio’s Nick Young reports

The Chicago Tribune reports defense called Aurora neurologist Dr. Pradeep Bhatia – who had been treating Kimberly Vaughn for tension and migraine headaches with two drugs. One of them, Topamax, was for a time required to carry a warning about an increased risk of suicide.

But Bhatia testified that he saw no signs of major depression or agitation in the woman, the Tribune reports.

Kimberly Vaughn — he told the jury — was “always smiling and cheerful,” the Tribune reports.

On June 14, 2007, Vaughn, his wife, and their three children – Abigayle, 12; Cassandra, 11; and Blake, 8, were on their way to a water park in Springfield from their home in Oswego.

Prosecutors say Vaughn shot pulled off Interstate 55 in Channahon Township and stopped on the frontage road. Then, authorities say, he shot his entire family inside their Ford SUV.

Vaughn’s wife was shot in the head, and each of his three children was shot twice. Vaughn himself suffered minor gunshot wounds in his wrist and leg.

Days later, Vaughn was arrested at the funeral services and charged with murder.

Vaughn and his defense team claim his wife shot the children and even fired at her husband’s head – only for the bullet to be deflected by his watch – before turning the gun on herself.