A Holts Summit man pleaded guilty to killing three people and injuring a fourth person in October 2010.
Joshua W. Maylee entered guilty pleas to three counts of first-degree murder and one count of first-degree assault.
Maylee admitted to killing 48-year-old Eugene A. Pinet, 57-year-old Jackie Pinet, and 46-year-old Jeffrey Werdehausen. Werdehausen's wife, Gina, was shot but survived.
Judge Kevin Crane sentenced him to four life terms in prison, three of which are without parole. Judge Crane ruled the sentences will run consecutively.
By pleading guilty, Maylee will no longer face a trial, which was scheduled to begin in September.
Authorities have said Maylee was involved in a theft ring with the two male victims and acted as a confidential informant until six weeks before the killings.