Attorneys for an officer charged with manslaughter in Freddie Gray's death sought Monday to discredit a state official's autopsy report, saying it was only a theory and not backed up by facts.

Defense attorney Joe Murtha, who is representing Officer William Porter, shouted pointed questions at assistant state medical examiner Dr. Carol Allan during her second day on the witness stand.

Prosecutors say Porter is partially responsible for Gray's death, which occurred a week after his neck was broken while he was in handcuffs and leg shackles in the back of a police transport wagon. Prosecutors say the officer failed to buckle Gray into a seatbelt and did not call for a medic when Gray indicated that he needed aid.

Porter is the first of six officers to go on trial in the case and faces manslaughter, assault, misconduct in office and reckless endangerment charges. If convicted on all of the charges, he could face about 25 years in prison.

Because there were no witnesses to Gray's injuries, the autopsy provides the most complete narrative of what happened in the back of the police van on April 12, and has served as a key part of the prosecution's case.

Defense attorneys say it is incomplete and speculative.

Both sides agree on this much: The van carried Gray on a 45-minute ride from his arrest to a police station, making six stops in total. During the second stop Gray, who was already in handcuffs, was secured in leg shackles and slid into the van on his belly, face-down. When Porter checked on Gray, during the van's fourth stop, the man was in the same position: face-down, with his feet pointing toward the van doors and his head toward the front of the wagon.

Allan wrote in the report that Gray's injuries suggested he had gotten up sometime between the second and fourth van stop, lost his balance due to an "unexpected turning motion, acceleration or deceleration" and was unable to brace himself because of his wrists and ankles were restrained.

Murtha questioned the findings.

"Do you have any facts, anything that's documented, between stops two and four?" Murtha asked.

"Other than he was injured, no," Allan replied.

When asked about the van's speed or the possibility of a sudden deceleration, she said "there's no evidence, because there are no witnesses."

"So you sort of made up this thing that you're calling evidence?" Murtha said.

"I didn't call it evidence," she said.

Allan added that Porter's lack of buckling Gray into a seat belt was "not a primary concern," when considering the man's injuries, perhaps an important admission considering the state's position that Porter's failure to secure Gray in a belt amounts to criminal negligence.

Allan also said that if the wagon driver, Caesar Goodson, had taken Gray to the hospital immediately after Porter had asked him to she would not have ruled Gray's death a homicide.

Goodson faces the most serious charge: second-degree "depraved-heart" murder. He will go on trial next year.

By raising questions about Allan's manner of death determination, Murtha sought to shift blame onto Goodson.

"If Goodson had followed orders and driven Gray to the hospital, you wouldn't have considered Gray's death a homicide?" Murtha said.

Allan responded, "that's correct."