He also said that the body belongs to a black girl.
Coroner Michael Murphy said he did not expect positive identification until Friday.
Jade was last seen by her family at about 5 p.m. Dec. 21 when Brenda Stokes picked her up for a shopping outing, police said. Police said Stokes was a trusted friend of the girl's father, and family members have told reporters that the two dated for several years.
Stokes, who also uses the name Brenda Wilson, was later arrested after she was accused of slashing a co-worker with razor blades at the Bellagio resort casino.
Stokes, 50, is now in jail and Jones said she has not cooperated in the investigation about the girl's whereabouts.
A passer-by called 911 about noon Thursday, and North Las Vegas police found a girl's body in unkempt brush near palm trees in a small traffic circle near Dorrell Lane and North 5th Street.
The location is a short distance from the northern 215 Beltway and about 10 miles from the downtown Las Vegas outlet mall off Interstate 15 where Stokes was to have taken the girl shopping.
Attempts by The Associated Press to reach family members on Thursday were unsuccessful.
Stokes picked up the girl about 5 p.m., and two hours later returned to another friend the red 2007 Saab sedan that she borrowed for the shopping trip, Jones said.
Later, Stokes got a ride with a friend to the Bellagio resort on the Las Vegas Strip, where she was arrested after allegedly attacking a female co-worker, Joyce Rhone, with a razor in each hand as Rhone dealt blackjack about 9:30 p.m.
Rhone, 44, was hospitalized with deep cuts on her face, including one from her ear to the edge of her mouth. A police arrest report said Rhone also had several smaller cuts around her right eye.
Records show that Stokes was being held Thursday on $60,000 bail at the Clark County jail on felony battery with a weapon, burglary and mayhem charges that could get her decades in prison.
She told a judge Wednesday that she had not obtained a lawyer. She was due again in Las Vegas Justice Court on Friday.
The arrest report says casino video shows Stokes attacking Rhone before a casino patron and security officers intervene. Officer Marcus Martin said the video is evidence that may be shown by prosecutors in court but will not be made public by police.
Police said Stokes later told investigators that she attacked Rhone over harassing phone calls and an unspecified betrayal that ended their seven-year friendship.
Stokes also told police she visited her doctor last week, seeking to be admitted to a hospital "due to feeling like she wanted to hurt someone."
She is reported to have told investigators she hadn't taken a prescription anti-anxiety drug on Friday, and that, "Sometimes people just snap."