Police also released photos of Genelle, one of which was taken at the intersection of East Tabor Avenue and Grande Circle in Fairfield minutes before she was last seen, Sgt. Matthew Bloesch said.
She was last seen wearing the clothes that appear in the photo: a gray sweater, blue jean-style leggings and a pink backpack.
Suisun City police said Genelle was reported missing around 5:45 p.m. Thursday by her foster home guardian.
Genelle was a student at Green Valley Middle School in Fairfield. School officials did not return phone calls today.
A man walking in Alan Witt Park found her body in the parking lot around 6:45 a.m. Friday, police said.
Fairfield and Suisun City police have been working non-stop on the case since her body was found, Bloesch said.
Police plan to hold a news conference Wednesday to discuss the investigation.
Fairfield police are focused on solving Genelle's murder, but they need your help. They've set up a tip line: 1 (707) 428-7345. Police are planning a news conference on Wednesday to give a progress report.