A man who had reportedly turned "to the bitter side" of life shot and killed a Montana Highway Patrol officer Wednesday near a small southwestern Montana town, prompting a manhunt that ended with the suspect found dead in his truck, police said.

The trooper, 23-year-old David DeLaittre, was gunned down in his vehicle on a roadway just off Montana Highway 2 near Three Forks at about 4:30 p.m., Gallatin County Sheriff James Cashell said.

Late Wednesday, Cashell said police found the gunman, Errol Brent Bouldin, dead in his 1999 green Ford F250 pickup outside Townsend, about 35 miles away.

"We don't know how he died yet and probably won't for a day or two," Cashell said.

More than 100 federal, state and local law enforcement officers from across southwestern Montana responded to the shooting. Authorities closed Highway 2 from the junction of U.S. Highway 287 to Interstate 90 at Three Forks.

The Gallatin County Sheriff's Office said Bouldin, 56, lived in Three Forks. Public records show he previously lived in Belgrade, a town about 20 miles away.

Belgrade police Sgt. David Keen said a warrant for Bouldin's arrest was issued on Dec. 3, 2009, on a contempt charge, meaning Bouldin either failed to appear in court or did not comply with a court order. Keen said he did not know why the contempt warrant was issued.

Debra Bouldin of Camp Verde, Ariz., told the AP in a telephone interview Wednesday night that her ex-husband was a dog trainer and drove a truck that fit the description of the one police found.

Debra Bouldin said she hasn't spoken to her ex-husband since he left Arizona in January 2006, after he nearly died from a rattlesnake bite the year before. Debra Bouldin said that experience left him a changed man.

"You know how when people have trauma they either become so thankful about everything about life or else they become bitter against life? Brent went to the bitter side," she said. "That was a very life-changing thing for him. What happened after that, I honestly can't tell you.

Cashell said more information would be released at a news conference scheduled for 2 p.m. Thursday.

DeLaittre was sworn in as a trooper in November 2008. He was initially stationed in Chinook and then transferred to Bozeman in April 2010, Department of Justice spokeswoman Judy Beck said.

The Bozeman Daily Chronicle reported that DeLaittre was also from Three Forks, where his parents and two sisters live.

Seven other Montana Highway Patrol officers have died in the line of duty, two of whom by shooting, according to the Association of Montana Troopers.