JOLIET, Ill. (CBS) – An Oswego man charged with killing his wife and three children in 2007 is set to go on trial starting in August.

Will County Judge Daniel Rozak set an Aug. 13 trial date for Christopher Vaughn, 37, who is accused of killing his wife and three children in their car along Interstate 55 near Channahon, while they were on their way to an amusement park in Springfield.

Prosecutors said they might need up to five weeks to present their case. Vaughn’s defense attorney said he might need another two weeks to put on a defense. Jury selection could take longer than normal because of the high-profile nature of the case.

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Authorities have said Vaughn shot and killed his wife, Kimberly, and their three children — 12-year-old Abigayle, 11-year-old Cassandra and 8-year-old Blake — on June 14, 2007, after he pulled over their SUV while on a family trip to Knights Action Park in Springfield.

Kimberly Vaughn was shot once under the chin. Prosecutors have said Christopher Vaughn also shot himself and tried to make it look like Abigayle shot him and the children before taking his own life.

Vaughn has maintained his wife killed their children, shot him, then killed herself.

Prosecutors also want to use online chat and e-mail messages to show Kimberly Vaughn hadn’t thought about suicide, nor did she think her husband had an affair in Mexico as he’s claimed. Rozak on Thursday allowed another set of e-mails into the trial.

Vaughn will be back in court March 23 as attorneys continue to debate what evidence jurors will have a chance to see.

While prosecutors haven’t set forth a motive in the murders, Vaughn’s wife had a $1 million life insurance policy that listed him as a beneficiary. Vaughn also confessed to an affair in December 2006 after a trip to Mexico. Court records show the couple had been fighting, and he would sometimes sleep at the office.

Prosecutors have said Vaughn was frustrated with his life and wanted to live in the Canadian wilderness.

Court records show police recovered a magazine article about staging crime scenes and “making the death appear to be a suicide” from Vaughn’s home after the killings.

Records also show Vaughn spent a half-hour at a Plainfield shooting range the night before the shootings, firing at targets with a gun later seized by police from between his dead wife’s feet.

The documents show the Vaughn family’s trip Springfield also was planned the night before the murders, reached after Vaughn’s wife accused him of spending too little time with their kids.

Meanwhile, an exotic dancer told police Vaughn had written her a poem about “ancient souls” and bad timing, and Vaughn might have explored the possibility of faking his death.

Finally, it appears the Oswego man wrote an ominous blog entry just weeks before the shooting about “wrapping up a few last things” before disappearing into the remote wilderness.

(The Sun-Times Media Wire contributed to this report.)