ALBUQUERQUE, N.M. (AP) — The New Mexico teen accused of killing his family and plotting to gun down Wal-Mart shoppers spent much of the day after the early morning slayings at his church, wandering the campus as dozens of Sunday school teachers were being trained on how to deal with a shooter, a security official said.

But it wasn't until hours later, former police officer and Calvary Albuquerque security chief Vince Harrison said, that he knew something had gone terribly wrong.

Harrison, who led the safety training Saturday morning, said he was called back to the church Saturday 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 say, they took the teen to headquarters. During questioning, they say 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. His father once served as pastor at Calvary.

They say 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 Saturday, but thought nothing of it until his arrest. He said officials then reviewed security video and found the teen had spent much of the day there.

He 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 schooled at his house.

"It was a familiar place to him," Harrison 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. Continued...