Bellefontaine, Ohio ? When the 49 students in Riverside High School’s class of 2005 marched into the gymnasium for commencement Sunday, they could not help but notice two empty seats.

Not until the ceremony was nearly complete did they learn classmate Scott Moody was dead. On Monday, students found out the rest of the news: that the 18-year-old was believed to have killed his grandparents, his mother, their other missing classmate and another family friend before shooting himself.

“Everybody was wondering, ‘Where are these two kids?'” school Supt. Bernie Pachmayer said Monday. “I think instinctively they knew something was wrong.”

Logan County Sheriff Michael Henry said he did not know if authorities would ever determine why Moody acted as he did, “but we’re going to try.”

Moody also shot his younger sister, who was in critical condition Monday.

The shootings came hours after a family party to celebrate the graduation of Moody and classmate Megan Karus at the farmhouse near this west-central Ohio town were he lived with his mother and sister.

Charlene Anderson, left, and Brandon Stewart, students at Riverside High School, look at a class photo of Paige Harshbarger in their yearbook in Bellefontaine, Ohio. Six people were found shot to death and a seventh was in critical condition after what authorities say was a murder-suicide. Paige Harshbarger, 14, was one of the victims of Sunday's shootings.

Students who saw Moody early Sunday before the shootings described him as being in great spirits and looking forward to graduation, Pachmayer said.

Sometime Sunday morning, Moody went to the neighboring farmhouse and killed his grandparents with a .22-caliber rifle, then came home where he shot the others then himself, Henry said.

Moody’s sister and the lone survivor, Stacy Moody, 15, called her stepsister and told her that she and her mother had been beaten up and that she could not wake her mother, Henry said.

Stacy Moody had been shot in the neck. She remained hospitalized Monday at Ohio State University Medical Center.

The stepsister, Nicole Vagedes, went to the house and called 911, telling emergency dispatchers about finding bodies throughout the house.

Henry said the grandparents, Sharyl, 66, and Gary Shafer, 67, were shot in their kitchen.

The bodies of Moody’s mother, Sheri Shafer, 37, and Paige Harshbarger, 14, a family friend, were found in upstairs bedrooms of their home, along with the body of Moody himself. Karus, 19, another family friend, was found on a living room couch.