WOBURN — With his father looking on, Orion Krause showed no obvious emotion Wednesday as he pleaded not guilty to killing his grandparents and their caretaker, but trembled visibly when his mother was identified as one of his four murder victims.

Krause, 23, allegedly used a baseball bat to attack his mother, Elizabeth Krause; her parents, F. Danby Lackey lll, 89, and Elizabeth Lackey, 85; and Bertha Mae Parker, 68, their caretaker.

The bodies of his mother and grandparents were found inside the Groton home where the elderly couple lived. Krause’s grandparents were mainly confined to reclining chairs in a small room next to the kitchen because of their age and health, Middlesex Assistant District Attorney Thomas A. Brant said Wednesday.

The bodies of the elderly couple and Krause’s mother were found in the kitchen and in the adjacent room, according to court records. Head wounds suffered by Krause’s mother and grandparents were “horrific, to put it mildly,” Brant said during Krause’s arraignment in Middlesex Superior Court on four counts of first-degree murder.

Parker was apparently the last to die and had escaped from the house and was running away when Krause allegedly caught up and attacked her from behind. Her body was found in a flower bed outside the home, authorities have said.

Krause was ordered held without bail by Clerk-Magistrate Michael A. Sullivan.

Following the brief court proceeding, Krause’s attorney, Edward Wayland, said he is considering mounting an insanity defense. “At the end of the day, mental illness will be the entire explanation for this,” Wayland said.

Before the court proceeding began, Orion Krause nodded in the direction of his father, Alexander, who was also in Ayer District Court last September when his son was first charged in the quadruple killing in the northeastern Massachusetts town.

Krause twice told a former music professor at Oberlin College that he intended to kill his mother, a threat Maine authorities passed on to Groton police Sept. 8, the Globe has reported. He called the professor shortly before the killings and told him, “I think I have to kill my mom,” according to documents filed in court. However, the Massachusetts department was alerted about 45 minutes after Krause allegedly killed the four people.

Groton police responded to the Common Street area around 5:52 p.m. that day, records show, after a neighbor alerted police that Krause was at his home, naked and splattered with blood, the Globe has reported. He allegedly admitted to murdering his relatives with a baseball bat.

Krause was arrested at the house and appeared in Ayer District Court, where he pleaded not guilty to four counts of murder and was ordered to undergo a mental health evaluation. He has since been declared competent to stand trial in district court.

One day before he allegedly killed his mother, Elizabeth Krause reached out to Maine authorities for help in locating her son, who she feared was suicidal.

He faces a maximum of four life sentences without the possibility of parole if convicted of first degree murder for each death.

John R. Ellement of the Globe Staff contributed to this report. Laura Crimaldi can be reached at laura.crimaldi@globe.com. Follow her on Twitter @lauracrimaldi.