Vaughn allegedly shot and killed his wife, Kimberly, and their three children -- Abigayle, 12; Cassandra, 11; and Blake, 8 -- inside the family's SUV on a frontage road near Channahon, Ill., on June 14, 2007. He was arrested at their funeral.
Vaughn pleaded not guilty and said his wife shot and killed their children and herself.
Last week, the jury was selected out of a pool of 34 men and women.
The trial is taking place at the Will County Courthouse, next door to another high-profile case, the Drew Peterson murder trial.
Speaking for the prosecution in court Monday morning, assistant state's attorney Debbie Mills opened her statement to jurors saying that "Christopher Vaughn was planning an exit scenario and in doing so he didn't want any responsibilities."
Mills went on to paint the picture of Christopher Vaughn as a man who was planning on moving to Canada to live in the wilderness. She said Vaughn went to the gun range the night before the shootings. She then claimed that despite blaming his wife, Kimberly, Vaughn unintentionally left enough blood evidence on his clothing and inside the vehicle where the shootings took place to prove that he committed the murders.
When his turn came defense attorney George Leonard described Vaughn as "a very private person. "He is an eccentric dreamer," said Leonard, whose personality makes him susceptible to suspicion. Leonard acknowledged that the Vaughns had problems in their marriage, but he then turned the tables on Vaughn's wife Kimberly. "She was happy on the outside, but troubled on the inside," he said.
The defense claim that medications that Kimberly Vaughn was taking medications to deal with migraines and depression are known to cause suicidal thoughts.
Following opening arguments, the state brought forth its first six witnesses, including first responders on the scene the day of the murders.
Graphic photographs of Kimberly Vaughn and the Vaughns' three children were displayed during questioning. Christopher Vaughn looked down as the photos were shown, but remained impassive during the entirety of the day's proceedings.