UPDATED: 8/20/2011 – 4:46 p.m.

CHICAGO (CBS) — Jurors in Christopher Vaughn’s family murder trial were shown graphic photos of the defendant’s dead wife and three children, and prosecutors claimed Vaughn planned the murders as part of an “exit scenario” to get away from a troubled marriage and start a new life in the Canadian wilderness.

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Vaughn is accused of killing his wife, Kimberly, and their three children — 12-year-old Abigayle, 11-year-old Cassandra and 8-year-old Blake — because he wanted to get away from his obligations as a husband and father.

Defense attorneys have argued Kimberly Vaughn was actually the one responsible for the shootings, claiming a mix of medications put her at risk of suicide and caused a big change in her personality.

A jury of four women and eight men was picked last week. Opening statements were presented Monday morning, and then the prosecution began calling its first witnesses.

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CBS 2’s Brad Edwards reports Vaughn sat stoic in a beige blazer as prosecutors outlined a ream of reasons why he wanted his family dead – including his affinity for strippers, and a desire to start life anew in the Canadian wilderness. Prosecutors allege Vaughn claimed to have made a scouting trip to plot his new life.

Calling it an “exit scenario from a troubled marriage,” Will County Assistant State’s Attorney Deborah Mills claimed Vaughn planned the murders and practiced with the murder weapon at a gun range the night before a planned family trip to a Springfield water park.

Before dawn on June 14, 2007, Vaughn and his family loaded into their SUV to drive to Springfield, but Vaughn allegedly pulled off the Interstate in Channahon, turned onto an isolated frontage road, and shot his wife and three children.

When police arrived, Vaughn claimed his wife was responsible for the shooting, and shot him twice before he fled the SUV.

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In a videotaped confession, Vaughn told police his wife was upset over his religious beliefs and his confession of adultery.

Vaughn’s defense team acknowledged the troubled marriage, but said he still loved his family and claimed Kimberly Vaughn was the one who pulled the trigger.

Defense attorney George Lenard said Kimberly Vaughn was at risk for suicide because of a combination of medications she was taking for migraines, high blood pressure and anxiety. He said there are emails showing Kimberly Vaughn told her doctor she was concerned the medications had caused a major personality change, and another email to a friend in which she calls herself “mommy monster.”

According to defense, in October 2005, Kimberly Vaughn emailed a friend, saying, “even though we are all human beings, we all have a little animal in us that can snap.”

Lenard also called Christopher Vaughn a “quirky, eccentric dreamer,” who was vulnerable to suspicion and aggressive police tactics.

The prosecution’s first witnesses set the scene. A number of first responders testified about finding the Vaughn family’s bodies in the family SUV on a road off I-55 in Channahon.

Prosecutors showed graphic photos of the victims’ bodies, prompting some jurors to cup their mouths and wipe away tears. The photos showed the three Vaughn

Kimberly Vaughn was found dead in the front passenger seat with a gunshot wound to her chin.

Their son Blake’s body was in the rear passenger’s side seat, the door smeared in blood.

Their daughter Abigayle’s body was found holding a Harry Potter book and a stuffed animal.

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The trial is expected to last six weeks.