Ibata Noric Hexamer, 44, was originally charged with 23 counts in 2010 after a special police taskforce found DNA evidence linking him to the four attacks, one of which dates back 15 years.
During the first attack, in 1995, Hexamer sexually assaulted a 13-year-old after forcing her into a stairwell at Lord Nelson Elementary School.
The second assault occurred in 2007, when Hexamer attacked two 14-year-old girls in Delta. The third attack took place in 2009, when Hexamer sexually assaulted a six-year-old girl in Surrey, and ordered the girl's 12-year-old-brother and 15-year-old friend to lie on the ground.
Hexamer worked as a personal assistant to Vancouver city councillors Tim Louis, Ellen Woodsworth, Tim Stevenson and Dr. Fred Bass, and was hired by Vancouver's Coalition of Progressive Electors as a political organizer in 2005.
He also worked on the 2006 federal election campaign as the database manager for the NDP in Vancouver Centre.
Following Hexamer's guilty plea, the Crown has dropped the remaining 17 counts related to the sexual assaults.
Hexamer remains in custody and will be sentenced in October.