The execution-style murders were one of the heinous murder cases they've worked on since it happened in 1998.
Jesus Ruben Moncada, 33, is believed to be one of the major gunmen involved in the killings.
He was arrested by federal authorities Thursday night outside his L.A. home and thought he was just being deported for being in the country illegally. He didn't realize that ICE had alerted Mexican authorities of his capture.
"When we approached him, he didn't show any reaction really because we told him we were there to take him into custody on immigration violations," said Virgina Kice from ICE.
Moncada now faces murder charges from a drug-related massacre in Ensenada that killed 19 people. Gunmen had raided a home of an alleged drug trafficker and kidnapped him and his extended family members. The gunmen lined up the victims and shot them execution style. Officials said eight of his victims were children.
Moncada is being held in a federal prison outside Tijuana. Eyewitness News reporters Lisa Hernandez and Carlos Granda contributed to this report.