But former police officer and Calvary Albuquerque security chief Vince Harrison said it wasn't until hours later that he knew something was wrong.
Harrison, who led the safety training Saturday morning, said he was called back to the church that evening after 15-year-old Nehemiah Griego told a pastor he found his family dead in their home.
"When I met Nehemiah, I knew something wasn't right," Harrison said Wednesday. "I could feel it, I could see it in his eyes and I could see it in his behavior and his demeanor so the red flags went up and that's when I called the sheriff's department."
Harrison, who had known the Griego family for about 10 years, said he drove the teen back to the family's rural southwest Albuquerque home to meet authorities, interviewing him along the way.
"He went into detail of where they were, where the guns were and he was very matter-of-fact, really cold, so I knew something wasn't right," Harrison said.
After finding the bodies, sheriff's officials said they took the teen to headquarters. During questioning, he confessed to shooting his mother and three younger siblings in their beds shortly after 1 a.m., then waiting in a bathroom with a military-style semi-automatic rifle to ambush his father upon his return from an overnight shift at a homeless shelter.
Investigators said he also told them he had reloaded the family's rifles and taken them with him in the family van with plans to randomly shoot more people.
"That sends chills down my spine," Harrison said. "But obviously, God had a different plan."
Harrison said several people spotted Griego at the church throughout the day and told him hello, thinking nothing of it until his arrest. Officials then reviewed security video and determined the teen had spent much of the day there, he said.
The video has been turned over to investigators, who have been working to piece together what led to the violence and what happened in the hours that followed.
Harrison said he doesn't know why Griego decided to come to the church, but that it was like a second home for the boy, who was homeschooled.
"It was a familiar place to him," he said. "I think if he did have in his mindset to do something foolish and start shooting people there also, I think his demeanor was tamed a little bit because he saw people there he knew."
Sheriff Dan Houston said Tuesday there was no indication Griego intended to harm anyone at the church. The sheriff also said Griego and his girlfriend had spent much of the day together.
A prayer vigil was held at the church Wednesday night for victims Greg Griego, 51, his wife, Sarah Griego, 40, and three of their children — a 9-year-old boy, Zephania Griego, and daughters Jael Griego, 5, and Angelina Griego, 2.
Before the start of the vigil, members of the crowd shared hugs and handshakes as photographs of the victims were displayed on large digital screens at the front of the church. An estimated 2,000 people attended and nearly every seat was filled before the start of the hour-long service.
"Our hearts break, Lord," Pastor Skip Heitzig told the crowd. "We, often in times like these, scratch our heads and wonder why. We are at a loss for words and we are certainly at a loss for explanation."
Heitzig shared stories about Greg Griego, who once served as pastor at Calvary. He said Greg was always ready to "get his hands dirty" and was dedicated to helping others find God through his work as a pastor and as a volunteer chaplain. Heitzig also urged the crowd to remember that forgiveness and restoration — two tenets dear to Greg — will be important as the community moves forward.
Relatives, in a statement Tuesday night, said they were heartbroken, and remembered the teen as a bright and talented musician who played guitar, drums and bass with the church choir. He also was a champion wrestler who dreamed of following his family's long tradition of military service, and a boy who accompanied his pastor father on rescue missions to Mexico, they said.
"We have not been able to comprehend what led to this incredibly sad situation. However, we are deeply concerned about the portrayal in some media of Nehemiah as some kind of a monster."
The statement, emailed by the boy's uncle, Eric Griego, called on the media and the public not to use Nehemiah Griego "as a pawn for ratings or to score political points."
"He is a troubled young man who made a terrible decision that will haunt him and his family forever," the statement said.