Desmond Turner, 28, reportedly told his co-accused James Stewart, 30, he planned to take guns and rob the family and "kill everyone in the house," Indianapolis Police Detective Leslie VanBuskirk wrote in a court statement.
Four adults and three children were gunned down Thursday night and the two men were arrested Saturday.
The Indianapolis Star said there had long been rumors in the neighborhood that the family had large amounts of cocaine and cash hidden in a safe in the house, but police said that turned out to be wrong.
"There was no money and no drugs in the house," Sgt. Matthew Mount told the newspaper.
The men face preliminary charges of robbery and multiple murder counts.
Turner told WISH-TV, Indianapolis, in an interview aired Monday he is innocent and was shocked when to discover Friday that police considered him the prime suspect.