DID DIABETES PLAY A PART IN THE DEATH OF CASEY JOHNSON???

The death of Johnson & Johnson heiress CASEY JOHNSON may have been caused, at least in part, by diabetes.  Casey . . . who died last week at the age of 30 . . . was diagnosed with diabetes as a child. 

--And a so-called "source" says police have a theory that incorporates the disease . . . quote, "The speculation is she came home after a night of partying and passed out without taking her meds or her insulin and that was the end of her."

--Despite Casey's history of drug problems, police say there were no obvious signs she'd taken any illicit drugs before her death.  There was also no evidence of suicide or any obvious medical problems.

--The results of toxicology tests are pending.

--Meanwhile, Casey's father . . . New York Jets owner WOODY JOHNSON . . . issued a brief statement yesterday via a team spokesman, saying, quote, "The Johnson family is mourning their tragic loss, and asks for privacy during this very difficult time."

--PARIS HILTON . . . who'd been friends with Casey since they were spoiled little rich kids . . . expressed her sorrow on Twitter. 

--She said, quote, "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 added, quote, "God has another Angel by his side.  Casey, we all Love and Miss you and know that you are in a better place.  R.I.P."

ONE OF CASEY JOHNSON'S FRIENDS BLAMES TILA TEQUILA FOR HER DOWNFALL: 

We've heard a few different theories about what caused CASEY JOHNSON'S death.  Here's one that's picking up steam:  TILA TEQUILA.

--Okay, maybe Tila didn't KILL Casey.  But there are those who believe Tila was responsible for Casey's downfall.

--Those would include Casey's former friend, Jasmine Lennard . . . who actually got Casey arrested for theft in November, because she allegedly stole jewelry, clothing and other items from Jasmine's home.

--Now, Casey had been getting into trouble for years . . . but Jasmine thinks hooking up with Tila was the beginning of the end for Casey.

--She says, quote, "Casey's family tried desperately to help her.  There was a car ready 24 hours a day to take her to the best rehab facility in the country.  When it came out that Casey had been arrested, she had nobody and was lost.

--"Tila got a hold of her and said, 'Hey, come out with me and we'll show them!'  For her to die with this reputation, it's just not her.  Tila is a sick, sick girl.

--"On one occasion [Tila] called me and a male friend screaming, saying people were breaking into her home.  When I arrived, she was naked with a kitchen knife screaming, but no one was there.  Everyone who crosses her path suffers consequences."

--Jasmine added, quote, "Casey was a fragile, beautiful, witty, wonderful girl who was desperately looking for love.  Did I love her?  Yes.  I tried so hard to save her but I couldn't."

--By the way . . . we've learned of the whereabouts of Casey's adopted daughter Ava.  Jasmine says that Casey's MOTHER assumed custody of Ava back in 2008, because she didn't approve of Casey's lifestyle.