Police believe Francisco Villalpando's pickup truck didn't even slow down before smashing into a motorcyclist waiting for a red light in a Tucson suburb on August 11.
John Kostelny, a 62-year-old motorcycle instructor, was crushed when the force of impact sent him careening into two other vehicles, and he later died of his wounds.
Villalpando, 44, who'd been driving on a suspended license, was uninjured in the crash. Officer Tim Nelson examined him for signs of impairment and noted "significant cues" of stimulant intoxication, such as high blood pressure, says Lieutenant Chris Olson, a special operations supervisor with the Oro Valley Police Department.
On August 21, Villalpando was indicated by a Pima County grand jury for 10 felony counts, including endangerment, aggravated DUI and criminal damage.
But when blood tests on Villalpando came back recently, they showed no evidence of any drug or alcohol in his system. On Friday, prosecutors dismissed their criminal case against Villalpando.
"We all find it very curious," says Olson. "No one was more floored than (Nelson). He really thought the guy was under a stimulant."
The raises obvious questions about the accuracy of drug recognition experts like Nelson, who can spot impairment that other DUI officers might miss. Nelson's also a DUI officer and a certified phlebotomist.
As Nelson was trained to do, he compiled all of the impairment cues Villalpando had presented and ran them through a matrix that helps make sense of the data. It indicated the suspect was under the influence of a stimulant, Olson says.
"Nothing was fabricated" in terms of Nelson's report, Olson adds.
Villalpando was otherwise healthy, and the notion that any medical issues could have contributed to the crash were ruled out.
Yet the evidence shows Villalpando apparently didn't see the motorcycle or the red light until it was too late.
"Clearly he was inattentive," Olson says. "We don't know why."
Villalpando hasn't made any statements about the crash.
Olson admits that mistakes by DRE officers are possible, but that blood tests of suspects typically back up the officers' educated guess. Nelson has a highly accurate record of successfully identifying the various drugs ingested by drivers, Olson says. A re-evaluation of the DRE program isn't planned.
"Every now and then, with a case like this, everybody's left trying to figure out what happened," he says.
Police are now looking at potential civil violations with which to charge Villalpando.
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