Eugene was last seen at his home in rural Fremont County, Colorado on June 21, 2004. Lynn Fish, his wife, stated he left their home angrily after and argument. She called Eugene's father a week later and told him Eugene had left; she stated she believed he left of his own volition. Lynn said Eugene had wanted to be free of responsibilities and he had smashed his computer and cut up his credit cards before leaving without the house. He left his cellular phone behind. She believed he was planning to go to Mexico or South America.

Eugene is a retired federal agent and has a pension of over $4,000 a month. He has not attempted to access it since his disappearance and Lynn is now collecting it in his stead. He has also not used his credit cards, passport and bank accounts since his disappearance. His parents have hired a private investigator to help locate him; the investigator believe Eugene met with foul play. He was born and raised New York, attended Siena College, and moved to Colorado in 2003 after his retirement. Most of his family lives in New York and he is the sole heir to his parents' estate, worth an estimated $500,000. Eugene was close to his family prior to his disappearance and called his parents every weekend.

Lynn has allegedly given inconsistent statements about Eugene's disappearance and has been uncooperative with the police investigation. She did not report him missing; one of his friends did so on September 1. Lynn stated that when Eugene left, he was driving his red 2000 Ford pickup truck. Eugene allegedly said he would send the truck back to her later. Lynn stated the truck reappeared in the Fish family's driveway days later, three miles inside the locked gate to the property.

Prior to his disappearance, Eugene had made statements to the effect that he was disillusioned by his retirement and his marriage. He and Lynn married in 1997 after cohabiting for four years. In January 2004, the police were called to their home to investigate a domestic dispute, but both Lynn and Eugene stated no violence had occurred, so no arrests were made. After his disappearance, however, Lynn told Eugene's father that her husband had been beating and shoving her.

Eugene's father died in 2007 at the age of ninety. In his will he left provisions for the foundation of a trust fund which will finance the search for Eugene. Eugene has previously lived in Utah and Texas. Although his family believes he met with foul play, police are investigating his case as a missing person rather than a crime.