Raleigh, N.C. — A woman who was killed in a May collision with a state trooper caused the wreck, although the trooper's speed and the fact that he didn't have his siren on at the time contributed to the severity of the crash, according to a Highway Patrol investigation released Monday.

Trooper J.D. Goodnight was trying to catch a Buick Skylark that was going south at 80 mph on U.S. Highway 29/70 in Guilford County on May 23, authorities said. Sandra Allmond was northbound on the highway on her way home from church and made a left turn at a green light onto River Road, turning into Goodnight's path.

The collision caused Allmond's 1995 Honda to split apart, and Allmond, 55, of Thomasville, was killed on impact.

One of three children she had in her car, Taylor Strange, 11, of Jamestown, died at Wake Forest University Baptist Medical Center in Winston-Salem. The other two children, Allmond's grandson, 11-year-old Elijah Allmond, and 9-year-old Steven Strange, were treated at the hospital and released.

The Highway Patrol released a 431-page investigative report that included testimony from witnesses and information from an examination of the vehicles, the intersection and an accident reconstruction team.

"As tragic as the situation is, we did do a thorough investigation and looked at every different angle," said Sgt. Jeff Gordon, spokesman for the Highway Patrol. "We know that this is tragic both for the family, but also its something that wears very heavy on the sleeve of the trooper."

Two witnesses said Goodnight had his blue lights on, but he hadn't activated his siren, as he chased after the Skylark. Goodnight told investigators that he didn't want to reach down and turn the siren on while speeding on the highway.

Investigators also spoke briefly with Elijah Allmond a few hours after the wreck while he was in the hospital, and he said he saw the patrol car coming toward the intersection with its blue lights flashing "and then Grandma turned," according to the report.

"No physical evidence or witness testimony has been obtained or serves to explain why Mrs. Allmond did not yield at the green light ... to the oncoming patrol vehicle displaying flashing blue lights," the report states. "The failure to yield the right of way to oncoming traffic is considered the causative factor in this collision."

Still, the report noted, "the speed at which (Goodnight) operated his vehicle contributed to the severity of the collision."

A preliminary report estimated that Goodnight was traveling at 120 mph down the highway and that he tried to brake and swerve to avoid the collision. His 2009 Dodge patrol car was traveling at 95 mph at the point of collision, the preliminary report stated.

The Highway Patrol has no policy that limits a trooper's speed during traffic enforcement efforts, Gordon said.

The investigative report also found that "had Trooper Goodnight been operating his vehicle's siren on this occasion, it may have provided an audible warning for motorists in the area."

Gordon said the patrol has since amended its policies to require troopers to activate both their blue lights and their sirens when they are trying to catch speeders.

"The last thing the Highway Patrol wants to do is put the general public's life in danger," he said.

Goodnight, who was injured in the collision, has returned to work, Gordon said.