On March 14, 2006, Senior Patrol Agent Nicholas D. Greenig was part of a two-man unit conducting operations to disrupt smuggling on the Tohono O'odham Reservation in Pima County, Arizona, within the Ajo Station area of responsibility. At approximately 8:10 p.m., the vehicle he and Senior Patrol Agent Roberto Easterbrooks were traveling in struck a large animal on Highway 86.

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Border Patrol agents working nearby responded to the scene of the accident to assist Police, Emergency Medical Services personnel, and the crew of a Life Flight helicopter. Agent Greenig did not survive the injuries sustained from the accident.

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Agent Greenig was 28 years old and was a graduate of the 535th session of the Border Patrol Academy.

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Agent Greenig had served with the Border Patrol for three years and was assigned to Ajo Station in Tucson Sector. He was raised in Laurel, Montana, where he attended public schools before he transferred to a private high school in Billings. He graduated with honors from Utah Valley State College in Provo and joined the Border Patrol in 2002. Agent Greenig was a graduate of the 535th session of the Border Patrol Academy. He was Senior Patrol Agent and a member of a special unit that targeted violent criminal organizations that smuggle people and drugs.

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At his memorial service, Greenig's family described him as a man of faith and dedication. He was the youngest of five children.