Police said in a statement Friday that 42-year-old Yvonne Robinson was taken into custody at her home in Carson.
Police say Robinson, a 13-year veteran who last worked as a juvenile division detective, leaked information to the Baby Insane Crips, who counted Robinson's brother-in-law among their members.
Detectives investigating the 2009 killing of a 19-year-old man learned that suspects in the gang were getting information that appeared to come directly from the police department, and launched the investigation that led to Robinson. She was put on administrative leave last year and fired in March.
A message left at a number listed in Robinson's name was not immediately returned.