Michael Andre Hall, 23, appeared Tuesday in West Valley Superior Court, and Judge Cara D. Hutson entered Hall's plea.
The San Bernardino County District Attorney's Office charged Hall on Monday with three counts of murder, along with gun and gang allegations.
"We're looking at 50 (years) to life on each of the counts," said Carlo DiCesare, the prosecutor.
Hall remains in West Valley Detention Center in Rancho Cucamonga in lieu of $5.5 million bail.
Attorney David Goldstein said he had been appointed to represent Hall shortly before the hearing and hadn't had a chance to examine the details of the case.
Hall was arrested Friday at his home in the 1000 block of West Springfield Street in Upland, police said.
His arrest came four days after the deaths of Brandon Perez, 31; Aaron Andrews, 25; and Albert Lamar Thomas, 25.
Police say Hall, Andrews, Thomas and Steven Carter went to rob Perez at his home in the 1000 block of South Magnolia Avenue. Perez and two of the suspected robbers were killed in a gunbattle.
Carter 34, of Upland, was arrested the day after the shooting. He has pleaded not guilty to the same charges Hall is facing.
Hall and Carter are scheduled to return to court today for a hearing.