Why Catherine Murch killed her children as well as herself?

A suburban St. Louis woman with a history of depression bought a gun two days before she killed her two children and herself while her husband was in another part of the house, authorities said Friday.

Emotional friends and neighbors stand outside the yellow tape as police detectives work the scene of a murder-suicide in a home in Glendale, Mo., on July 30, 2012. Nearly two dozen investigators with the St. Louis Area Major Case Squad were looking into the shootings deaths of a suburban St. Louis woman and her two children, police said Tuesday. Police haven't officially released the victims' names, but have said the children who were killed were ages 11 and 9. (AP Photo/St. Louis Post-Dispatch, J.B. Forbes)

Mitchell Murch II called police Monday to report that he heard shots. Police who responded found 42-year-old Catherine Murch in the kitchen, 10-year-old Mitchell Murch III elsewhere on the first floor and 8-year-old Mary Claire Murch on the second floor of the house the well-to-do suburb of Glendale.

Police questioned Mitchell Murch II but said they believed the case was a murder-suicide. Still, nearly two dozen investigators with the St. Louis Area Major Case Squad were assigned to the case.

During an emotional news conference Friday, Lt. Tim Fagan said although investigators were still awaiting toxicology results, they were confident the shooting was a murder-suicide, as was originally reported. He pointed to three key pieces of evidence in determining that Catherine Murch was responsible for the shootings: an autopsy suggesting her wounds were self-inflicted, a receipt showing she bought the handgun used in the shootings from a St. Louis business two days earlier, and her longtime battle with depression. He said no suicide note was found.

Catherine Murch

Fagan said Catherine Murch had been fighting depression for several years but her condition seemed worse recently. He also said the family had been under some financial strain but didn't elaborate.

"She was having a difficult time," Fagan said.

Fagan said the size of the investigation was necessary to "get a very clear understanding of what happened." He had to stop and compose himself for several seconds when asked why Catherine Murch killed her children as well as herself.

"I have a picture of someone who loved her children very much. I know that's difficult for all of us...." He paused and appeared to be choking up. "Difficult for all of us to understand."

Fagan said the shootings happened in quick succession. Mitchell Murch III was shot several times, but Mary Claire and Catherine Murch were both killed by single shots.

"I don't know if there was much opportunity for him to intervene," Fagan said, referring to the children's father.

Police said Mitchell Murch II was reading inside the home when he heard gunfire. When first responders arrived, they found him trying to resuscitate his son.

The deaths shocked the affluent neighborhood, where the Murches' stately, two-story brick home sits on a large, neatly manicured lot. Court records show the couple paid $764,900 for the home in 2007.

Catherine Murch graduated from the University of Missouri in 1992 with a degree in political science and received a nursing degree from Saint Louis University in 1994. Online records indicate she was a registered nurse.

Mitch Murch II, 43, graduated from the University of Missouri, also in 1992. He owns a maintenance management company.

The family was active in Mary Queen of Peace Catholic Church in nearby Webster Groves, and the children attended Mary Queen of Peace School, where Catherine Murch was a frequent volunteer.

Private funeral services are scheduled for Saturday at Cathedral Bascilica in St. Louis.