A man charged with four counts of first-degree murder, for allegedly using a shotgun to kill an ex-girlfriend, her baby and two acquaintances with a speed that astounded investigators, sobbed as a judge entered a not guilty plea on his behalf Friday.

Jason D. Smith (search), 28, of Dupo, said nothing during his brief arraignment, when St. Clair County Associate Judge Brian Babka ordered that he be assigned a public defender. Smith continued crying as he was led away in shackles to jail, his bond set at $4 million.

The criminal complaint filed by prosecutors Friday did not provide a motive for Wednesday night's killings. St. Louis Major Case Squad's Norman Venable told reporters Friday the killings followed "a domestic problem" between Smith and 19-year-old Nicole Willyard, whom Smith dated.

Police responding to reports of a burglary found the bodies Wednesday night in a basement apartment in Belleville, a St. Louis suburb.

"We don't know the motive. It'd just be speculation on our part," Venable said.

Venable said it was unclear whether Smith was the father of the slain 2-month-old baby, who also was named Jason D. Smith.

Belleville Police Chief Terry Delaney said investigators assume Smith first fired through the apartment's window at Willyard, who authorities said appeared to be the target of the rampage, as she watched television. She was shot in the head and chest, and her body was found in a recliner in the home's living room, according to prosecutors.

Investigators suspect Smith then crawled through the shattered window and killed Mary Cawvey, 19; Brandon Lovell, 23; and the baby, Delaney said. The boy's body was found in an infant seat.

Venable said Smith acted alone when he stormed the basement apartment and prompted neighbors to report a burglary in progress — just two minutes before officers arrived. During that span, Venable said, Smith fired off at least eight blasts from the shotgun, suggesting he may have had to reload at least once.

Cawvey had rented the apartment for about five months. Less than two weeks ago, she let Willyard — a friend from high school — and the baby live with her, Delaney said. Lovell and Willyard were longtime friends, according to a cousin of Lovell's.

Cawvey's own 2-year-old boy was staying with her father and was not home at the time of the slayings, Delaney said.

Lovell, who was visiting the apartment, was shot in the head, chest and back, according to the criminal complaint. Cawvey was shot in the head and chest, and the baby was shot in the head.

The victims were dead and the gunman had bolted by the time officers arrived, Delaney said, remarking that the gunman acted so quickly that "we could have been on the street corner" when the gunfire erupted and not caught the suspect at the scene.

"There's a strong possibility the suspect passed our police cars within seconds," Delaney said. "I just don't know how you'd prevent something like this."

Smith was arrested about 2:45 a.m. Thursday in Red Bud and was held at an area hospital for facial and arm injuries Venable would not discuss on Friday. In court, Smith had white bandages around both wrists.

He declined to answer reporters' questions as he was led out of the courtroom.

Smith has had previous scrapes with the law, St. Clair County court records show. In August, he was ordered to pay $175 in fines and court costs after admitting he illegally consumed alcohol as a pedestrian and obstructed a police officer in Cahokia, another St. Louis suburb.

Smith also has been fined for battery dating to a March 2004 incident in Dupo, as well as for criminal damage to property in that town in 2000. He also previously pleaded guilty to charges of criminal trespassing and disorderly conduct.