Andrew Rentschler

“I am a biomechanical engineer and accident reconstructionist.”

Concise description of the expert's field at the start of the qualification examination.

“So specifically, overall, I was tasked from the biomechanical standpoint to determine, or see if it's possible to determine how the injuries in this case occurred, and part of that was to determine whether the injuries, the head injury and the arm injuries resulting from contact with the Lexus in this case.”

States the scope of his requested biomechanical analysis.

Dr. Rentschler described his education, engineering practice, and experience in biomechanics and accident reconstruction as the defense established his qualifications.

On cross-examination, Dr. Rentschler said ARCCA's opinions were based on the materials listed in its report and that he personally reviewed the information provided.

“So both the physical evidence as well as looking at the biomechanical aspects of it are inconsistent with that head injury occurring due to impact with the rear of the Lexus.”

Rentschler stated his conclusion about the head-injury mechanism before the court later clarified the limits of his case-specific causation testimony.

“But, when you look at the abrasions that were noted in this case, they all appear to be the same force, generally the same direction and of the same severity, which would be inconsistent, in my opinion, with being struck at 25 miles an hour.”

He contrasted the observed abrasions with the injury pattern he said he would expect from the hypothetical vehicle impact.

“And that's not going to happen if you just hit the arm. It's not enough force. It's not the right mechanism to actually cause the body to somehow move that far over.”

He explained his general biomechanics view of how arm contact differs from a force acting at the body's center of mass.

“I didn't have enough evidence based on what I was provided.”

The expert acknowledged a limit on the evidentiary foundation available for his analysis.

“So there's numerous, almost infinite possibility of different scenarios that could result in that type of an event.”

Rentschler described alternative mechanisms for a backward fall and head injury.

“No, if you look at them it's like one minute, two minute, and three minute, and in that time period, according to my records, I have like a 21 minute phone call that encompasses most of that time.”

He disputed the characterization of 23 separate calls by contrasting it with his own phone records.

“It certainly helped prepare to understand what was going on during the trial, yes.”

He acknowledged that updates from Department of Justice personnel helped him understand trial developments before his testimony.

“A — that the force wasn't sufficient, or the acceleration wasn't sufficient, to produce enough force to cause a skull fracture at 15 miles an hour.”

Core expert opinion: drop testing showed a 15 mph tail light impact cannot generate enough force for an occipital skull fracture.

“it would take about 1,400 to 1,600 lb of force to cause an occipital skull fracture”

Establishes the biomechanical threshold that the defense argues a tail light impact at 15 mph cannot reach.

“to have an impact to the back of the head, you really couldn't have someone positioned in such a manner to strike just the head and not have subsequent concomitant injury to the neck or any other part of the body”

Explains Rentschler's opinion that a head-only strike would require accompanying injury to the neck or another part of the body.

“my opinion was that the injuries would be inconsistent — or the injuries that Mr. O'Keefe sustained on his right arm and didn't sustain — would be inconsistent with actual interaction with the tail light”

Second prong of the defense expert opinion: arm abrasions also inconsistent with tail light contact, and expected fractures were absent.

“I counted 36 different superficial abrasions on his right arm.”

Establishes a key discrepancy: 36 abrasions versus only 9 holes in the sweatshirt sleeve, undermining the tail light contact theory.

“So at 24 miles an hour, for the arm, the acceleration is 302 g's, and for the hand it's about 435 g's.”

Quantifies the forces involved, establishing that impact at alleged speed would far exceed fracture thresholds for hand and arm bones.

“It is my opinion that it is not consistent with contacting and fracturing the tail light cover.”

Core defense opinion rejecting the prosecution's mechanism of injury for the arm.

“There was no bruising. There were no lacerations. There was nothing at the alleged point of contact which would indicate an impact that produces thousands of pounds of force on the arm. No evidence of it whatsoever.”

Summarizes the totality of absent expected injuries that undermines the vehicle strike theory.

“I do not. No, sir.”

Answer to Brennan's question whether Rentschler had a source saying the Hybrid III arm was suitable for determining superficial abrasions. It did not resolve his broader analysis, which Rentschler said Brennan later misrepresented.

“Some of those appear sharp. Could possibly cause a laceration. Sure.”

Limited concession that some microscope-viewed fragments appeared sharp and could possibly cause a laceration.

“No, I don't think he even got hit by the car, sir.”

Reveals Rentschler's advocacy position rather than neutral expert analysis, volunteering his belief about the ultimate issue unprompted.

“I said it certainly helped prepare me to understand what was going on during the trial. Yes.”

Brennan used Rentschler's prior sworn answer — that receiving information helped him prepare — to challenge his trial testimony about what he received and its effect.

“The shard can't come out and then make a right turn and then somehow embed itself on the left side of the nose. That's entirely inconsistent with the fracture and how the glass and the cover would actually move.”

Rentschler gave his trajectory opinion under the tail-light-strike geometry he described.

“If the injuries don't match up, if you can't even prove what happened, then you can't use information or evidence — if you have no idea how it got there — to try and prove what you don't even know happened. It scientifically makes no sense.”

Rentschler stated his methodological view that injuries and collision mechanics must first support an impact before scene items can establish one.

“No, they are not.”

In response to Jackson's question, Rentschler said O'Keefe's injuries were not consistent with the subject Lexus, and then affirmed that opinion to a reasonable degree of scientific certainty.

“Well, I don't believe that's consistent with the evidence and what occurred. I mean, someone can get clipped by a car, sure. But in this case, no. I don't believe the evidence indicates that's what occurred.”

Rentschler acknowledged that clipping is generally possible but said it did not fit the case evidence.

“Oh, I — I don't know. There's no evidence of how it broke.”

Rentschler said he did not know how the taillight broke.