Michael Plummer, 20, his girlfriend Adah Pearson, 18, and Plummer's 21-month-old nephew Julio Rangel, were shot to death in a Normal Heights apartment on Sept. 4, 2000.
The child’s parents were home during the shooting but weren't wounded, police said.
Police at the time said it appeared that the shooting started when Plummer went to an apartment next door to buy some drugs and returned to his own unit without paying for them, the San Diego Union-Tribune reported.
A man was extradited from Mexico and charged with killing a couple and their toddler in 2000 in San Diego. (Fox News)
The dealer followed and demanded money, then opened fire with a rifle from outside the door, spraying 14 shots into the living room, police said.
Contreras was believed to have fled to Tijuana after the killings. Police didn't immediately say when he was arrested.
Contreras was charged in 2007 with three counts of murder with special-circumstance allegations that the killings were committed with a rifle and while lying in wait.
It wasn't immediately known whether he had an attorney to speak on his behalf.