Prosecutors said the young man, accompanied by 19-year-old Kendrec McDade, confessed to stealing a laptop from a car on March 24. A 911 caller, Oscar Carrillo, told police the thieves were armed.
Fearing for their safety, officers shot and killed McDade when he reached toward his waistband. Police said Carrillo later acknowledged that he lied about the gun to speed up officers' response.
The 17-year-old made the admission Tuesday to two felony counts of burglary, one count of grand theft and a misdemeanor count of failing to register as a gang member, Los Angeles County prosecutor Anna Phillips said. He wasn't identified because of his age.
The Associated Press contributed to this report.