As for the biggest question, he concluded his report with these frustratingly ambivalent words:
"The fatal injury could be self-inflicted or at the hands of another and satisfy the factors of contact wound, wound path, supine subject [Drenth], and the post-injury flight path of the plastic wad.
"Regrettably, the central issue of suicide vs. homicide was not answerable as of this writing."
Questions of motive and opportunity always arise first in investigations of violent deaths.
Those who insist that Sean Drenth was murdered have been unable to provide any viable motive for homicide other than the speculative.
Those who lean toward a suicide theory also lack sound evidence.
If Sean Drenth did kill himself, his sole known motivation may have been his role in an off-duty scandal that originally ensnared more than 25 Phoenix PD officers.
In 2008, the state Attorney General's Office started a criminal investigation of allegations that the cops were paid for security work they didn't perform in full at a Phoenix housing complex.
The probe seemed to go dormant until it re-emerged shortly before Drenth's death with a pared-down suspect list of four officers, including Drenth.
Clearly, the state's prime target was George Contreras, coordinator of the off-duty officers, who abruptly quit the Phoenix PD after 17 years on the force as the investigation moved forward in 2008.
Drenth almost certainly knew he was about to be indicted. Rumors about the off-duty case were flying around the department, and a close friend of the sergeant's, Lieutenant Chris Moore, had firsthand information that an indictment was coming down soon.
Still, no one has confirmed that Drenth was aware of the pending indictment, much less was expressing trepidation about it. (He would have been charged with "stealing" $1,065 allegedly paid to him through Contreras.)
To the contrary, everyone interviewed by police after Drenth's death claimed that the sergeant — a cheerful man with a distinctly offbeat sense of humor — was especially positive in his last days after a transfer back to the South Mountain Precinct.
"I know Sean would have said something to me about that off-duty bullshit bugging him if it was," says his lifelong friend Tom Kilstrom. "But he was fine. He was fine."
Had Drenth donned what police suicide expert and retired cop John Violanti calls the "mask of contentment," when he resolved, for whatever reason, to end his own life?
No way, says his mother, a straight-talking woman who is a project manager for a large bank.
"Sean would have been pissed if he got indicted," Diane Drenth says. "But he hadn't done anything wrong other than to trust George Contreras on that stupid off-duty thing. It wouldn't have been the end of his world."
In November 2010, a grand jury indicted the three surviving officers and Contreras on felony theft charges within weeks of Sean Drenth's death.
But state prosecutors dropped the case against three of the officers months later after a county judge remanded it to the grand jury. (Earlier this year, the trio sued the Attorney General's Office and others for what they contend were bogus charges against them.)
Contreras still faces charges of theft and illegal control of an enterprise — the off-duty operation he was running.
Steve Vernier had just gone on duty on the evening of October 18, 2010.
It was about 10:30, the Phoenix sky was clear and crisp, and the moon was almost full.
Within minutes, Vernier, an assistant with the Capitol Police, came upon Sean Drenth's body in the secluded alley at 18th Avenue and Jackson.
Vernier is not a sworn officer and wasn't carrying a weapon. His job included patrolling around state government buildings.
As he began his rounds, Vernier heard over his radio that an on-duty Phoenix officer wasn't responding to communications calls from dispatchers.
At 10:54 p.m., he drove toward the alley, still on routine patrol. The alley is north of fenced-in railroad tracks and south of a state-employee parking lot, which also is fenced in.
During his normal 10-hour shift, Vernier might patrol that area three or four times.
Accessible only from the east, the V-shaped alley begins at a volleyball court, narrows, and dead-ends about 100 yards west at the tip.
The floor of the eastern half of the alley is dirt and sand. Much of the west half is paved with cracked asphalt and is very dusty.
Police said later that homeless people used to frequent the immediate area. But Vernier hadn't seen anyone other than Phoenix police officers in the alley in years.
On-duty cops favored the site as a seemingly safe place to write a report or relax for a few minutes. It appeared secure because of the six-foot-high chain-link fences topped with barbed and concertina wire on the north and south sides.