The autopsy of Johnson & Johnson heiress Casey Johnson is inconclusive and toxicology tests have been ordered.

Los Angeles County coroner spokesman Craig Harvey says examiners on Tuesday deferred the cause of death for the daughter of New York Jets owner Woody Johnson.

FOX411 EXCLUSIVE: Casey Johnson lied about daughter to get money, says friend.

Her cause of death was under investigation, but there were no signs of foul play, police spokesman Officer Gregory Baek said.

Johnson was diagnosed with diabetes as a child, but it was unclear if that may have played a role in her death.

Additional tests, including a toxicology screening, could be ordered if the autopsy fails to determine how she died.

SLIDESHOW: Casey Johnson's short life in the fast lane.

"We continue to inquire into prior medical history," Craig R. Harvey, a spokesman for the coroner's office, said in an e-mail.

Johnson was the daughter of Jets owner Robert Wood "Woody" Johnson IV. He is also chairman of the Juvenile Diabetes Research Foundation and co-authored the book, "Managing Your Child's Diabetes."

Woody Johnson learned of his daughter's death just one day after his team clinched a playoff spot for the first time in three seasons.

Johnson family spokesman Jesse Derris released a statement saying, "The Johnson family wishes to thank everyone who has expressed condolences and support during this time.  Your thoughts and prayers are deeply appreciated."

EXCLUSIVE: Diabetes being eyed in Casey Johnson's death, source says.

Jets head coach Rex Ryan opened his press conference Tuesday by offering condolences to the owner.

"It's obviously a tragedy for Mr. Johnson and his family," Ryan said.

Casey Johnson had no role in the health care products company that her great-great-grandfather founded in 1886, even though she and her two younger sisters were heirs to the fortune.

The family's involvement with the corporation ended decades ago.

"We have expressed our condolences to the Johnson family for their tragic loss," Johnson & Johnson spokesman Jeff Leebaw said.

Like her friend and former high school classmate Paris Hilton, Johnson's exploits were detailed in tabloid reports of partying and sexual escapades. Johnson became a staple of the New York Post's Page Six, the gossip column where she was mockingly dubbed the "baby-oil heiress."

Johnson told Vanity Fair in a 2006 interview that her decision to turn down Hilton's invitation to be her co-star on "The Simple Life" reality show was "the stupidest mistake of my life."

In a Twitter posting Tuesday, Hilton said she was devastated by the death of her friend.

"In bed crying, looking at baby pictures of Casey, Nicky and I. I feel so upset. I feel like I've lost a sister. My heart is broken. Miss her," she wrote.

Johnson and Tila Tequila canoodled and announced they were engaged in a Web video last month. Tequila referred to Johnson as "my Wifey" in a Twitter posting after Johnson's death.
Johnson was recently arrested for investigation of stealing $22,000 in lingerie, mail, jewelry and other items from the Hollywood home of model friend Jasmine Lennard.

SLIDESHOW: Casey Johnson's bisexual fiancee Tila Tequila.

She pleaded not guilty last month to burglary and receiving stolen property, and had a preliminary hearing scheduled on Feb. 2, district attorney's spokeswoman Jane Robison said.

Johnson also was reportedly in a custody fight over her adopted daughter with her mother, Sale Johnson.

Casey Johnson adopted the child as a baby from Kazakhstan in 2007 and named her Ava-Monroe after her idol, Marilyn Monroe.

"I see a lot of similarities between us," Casey said about Monroe in the Vanity Fair interview.

"Her life makes me sad. I don't think she was very happy.

"They thought she was some dumb blonde, and she wasn't. She was a smart, smart broad. And I think that sometimes people look at me and think, 'Oh, Casey Johnson, she's stupid, she's blonde, she's an heiress, blah, blah, blah."'