Under the plea agreement, Johnathan Cruz, 20, will be sentenced to three consecutive sentences of life without parole for the May 2016 murders of Billy Boyd, Jay Higginbotham and Jose Alberto, the Marion County Prosecutor's Office said in a statement.
He also will be sentenced to 16 years for an armed robbery during the crime spree. The sentences will run concurrently. Formal sentencing is scheduled to take place on May 11.
Cruz's attorney could not be immediately reached for comment.
During the investigation into the killings Cruz told witnesses that he was "purging," a reference to the horror-thriller film "The Purge, prosecutors said.
The three victims were fatally shot on the east and north sides of Indianapolis. Marion County Prosecutor Terry Curry said shortly after the killings that they appeared to be random, the Indianapolis Star newspaper reported.
In the 2013 film, which stars Ethan Hawke, the U.S. government allows an annual 12-hour period where all crimes, including murder, are legal.
The movie was the first in what would become a popular franchise. "The Purge: Election Year" was released last July. The fourth installment is set to be released in July 2018, the Hollywood Reporter said in February.
(Reporting by Timothy Mclaughlin in Chicago; Editing by Bill Trott)
(This story has not been edited by NDTV staff and is auto-generated from a syndicated feed.)