An Iraq war veteran suspected of killing his ex-girlfriend and her pregnant sister in Michigan fatally shot himself in a remote West Virginia cabin after seeing investigators closing in, authorities said Wednesday.

Deputy marshals and Tyler County sheriff's deputies were approaching the cabin near Sistersville Tuesday evening when they saw Thomas Fritz run inside holding a rifle, said Alex Neville, a deputy marshal in Clarksburg. Seconds later, they heard a gunshot.

Not knowing whether the 38-year-old Fritz had shot himself or fired on them, special units from Wetzel County and the State Police who were better equipped to deal with the potential standoff were sent in to help, Neville said.

"It would not have been prudent for the deputy marshals or local law enforcement to engage him in that cabin, with several hundred yards of open field around the cabin," Neville said. "To approach it would not have been a good tactical approach on our part."

Several hours after the shot rang out, officers fired tear gas into the cabin and stormed in. They found Fritz dead of a self-inflicted gunshot wound in a rear bedroom, as well as two assault rifles, a shotgun and a gas mask, Neville said.

Authorities warned after the Friday killings that they considered Fritz armed and dangerous. Fritz served in the Ohio National Guard beginning in 1997 and later the Army Reserve. He then spent nearly a year in Iraq with the guard's military police unit from the spring of 2003 through early 2004.

Fritz had once worked for the man who owns the cabin, which is in a remote area near the Ohio border about 80 miles southwest of Pittsburgh, Pa., and he had been there several times, Neville said.

"He was familiar with the area. He returned there obviously to hide," he said.

Authorities contacted the cabin's owner, who was not there at the time and whose name they didn't release, to get its layout.

Authorities said Fritz's ex-girlfriend, Amy Merrill, broke up with him about three weeks ago. On the night of the killings, he went to her Blissfield, Mich., home, where he had lived with her since last winter, to speak with her. The two had a child together, who is a toddler, and Merrill's two sons from a former marriage also lived there.

Police say Fritz shot Merrill, 33, her 24-year-old sister, Lisa Gritzmaker, who was eight months' pregnant, and their mother, Robin Lynn McCowan, who were all at the home. The sisters died and McCowan is recovering from surgery at a hospital.

The sisters grew up in the Blissfield area and were well known. Merrill took her two oldest boys to youth baseball games and Boy Scouts meetings. She and her sister were extremely close, friends said.

Before moving in with Merrill, Fritz was living in Sylvania, Ohio, a Toledo suburb where he grew up, which is about 12 miles from Blissfield.

In 2004, the year he returned from Iraq, Fritz received an associate of applied science degree in criminal justice from Owens Community College, near Toledo.

In 2006, Fritz was convicted of sexual battery, deemed a sex offender and sentenced to a year in prison in Ohio. Paul Dobson, a Wood County, Ohio, prosecutor, said a woman accused Fritz of having sex with her at a party while she was passed out.