GROTON — Orion Krause, the 22-year-old Oberlin College graduate accused of four counts of murder, apparently used a baseball bat to kill his mother, his grandparents, and their caretaker at a home here last week, prosecutors said Monday.

The victims in the quadruple homicide were identified by Middlesex District Attorney Marian T. Ryan as Krause’s mother, Elizabeth Krause, 60; her parents, F. Danby Lackey III, 89, and his wife, Elizabeth Lackey, 85; and their caretaker, Bertha Mae Parker, 68, a health aide who had recently begun caring for the elderly couple.

Krause was ordered held without bail in the slayings and was committed to Bridgewater State Hospital, a psychiatric facility run by the Department of Corrections, so that doctors can evaluate whether he is competent to stand trial. Krause pleaded not guilty.

The killings have shaken this small town, about 40 miles northwest of Boston. The town had not experienced a murder in more than 20 years.

At a news conference after the arraignment in Ayer District Court, Groton Police Chief Donald Palma Jr. assured residents the killings were not random.

“It’s a horrific situation that we are not used to dealing with,’’ Palma said. “I want to assure the town that you are safe.’’

Also Monday, prosecutors disclosed that Krause had abruptly left his family’s house in Rockport, Maine, late Thursday night. Worried, his mother called police. But Krause called her early the next morning, saying he was in the Boston area some three hours away and needed a ride back home.

Elizabeth Krause agreed to pick up her son. On their way back to Maine, they stopped by her parents house in Groton. Police later found the four victims, who had been beaten to death.

Orion Krause’s appearance in court Monday was brief. As he stood with his hands cuffed behind him, several of his family members watched him from the back row of the courtroom. One of them, a young woman, had brought a tote bag full of clothes.

“They’re for him,’’ she whispered to a court officer, who took the bag.

Krause showed little reaction during the hearing. As Judge Margaret R. Guzman ordered that he be held at Bridgewater State Hospital, some of his relatives wept.

His next court hearing was scheduled for Oct. 30.

Family members left the courthouse without answering questions from reporters. They drove away in two BMWs, escorted by a Groton police SUV cruiser.

At the request of prosecutors, Guzman impounded the police report for the case. Ryan, the district attorney, said the report was “part of the ongoing investigation in these preliminary stages.’’

“We are only 72 hours into this investigation and the police are still actively conducting interviews and collecting evidence,’’ said Meghan Kelly, a spokeswoman for Ryan. “Releasing police reports at this time would compromise the integrity of the investigation.’’

At the news conference, Ryan declined to say whether Krause has a criminal record or a history of mental illness. She did not offer a motive for the slayings.

Krause’s grandparents were found dead inside their house, along with Krause’s mother. Parker was found outside the house.

After the killings, Krause allegedly made his way to a neighbor’s house where he told Wagner Alcocer “Help me please, help me please. I murdered four people.’’

Alcocer said Krause was naked, covered in mud, and had blood on his face. He offered Krause a chair and a drink of water, then called police.

When he asked Krause where his clothes were, he said “I left them in the woods.’’

Krause, a skilled jazz drummer whose college friends described as polite, quiet and even-keeled, has a twin brother. In court, a young man dressed in a suit jacket and tie sat in the back with the rest of Krause’s relatives. He bore a striking resemblance to Krause and remained standing when Krause was brought into court. Next to him stood a gray-haired man who held back tears as Krause stood before the judge.

A court officer walked over and gently asked both men to sit down for the rest of the proceedings.

John R. Ellement contributed to this report. Ellement can be reached at ellement@globe.com. Follow him on Twitter @JREbosglobe. Maria Cramer can be reached at mcramer@globe.com. Follow her on Twitter @globemcramer.