Los Angeles police responded to the single-vehicle crash around 2:30 a.m. in the 11200 block of Ventura Boulevard.
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Investigators said Butler's Range Rover was traveling between 60 and 90 mph around a curve on Ventura, where the posted speed limit is 30 mph.
The vehicle lost control, sheared three parking meters, careened through a concrete wall and rolled over several times before landing in a nearby parking lot.
The Los Angeles County coroner's office identified Butler as the driver but did not immediately release the passenger's name. Several of Butler's former teams and teammates issued a statement of condolences for him and LaBelle, a former "American Idol" contestant.
"The L.A. Clippers are deeply saddened by the loss of Rasual Butler and his wife, Leah LaBelle," the team said in a statement. "Rasual will long be remembered not only for his accomplishments on the court but for his vibrant personality, positive outlook and the compassion he had for everyone around him."
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Officials believe excessive speed was a factor in the crash.
"This is a horrific scene and a tragedy that could have been prevented. This is clearly, at this point, an issue related to speed. It's something we all have control over," said LAPD Capt. Andrew Neiman.
Investigators were looking into whether drugs or alcohol were a factor in the wreck.