The three-term House member from Murray said he questions whether Gill is a cop hater based on his "pattern of behavior and conduct."
He also reiterated that Gill's upbringing in India has "tainted his handling of use of force issues" because Gill grew up seeing police brutality in India and has spoken publicly about it before, Bennion said.
"His being harder on cops than he is on criminals is a legitimate issue," Bennion said.
Bennion's comments originally came after Gill announced Thursday that he found the Nov. 2 fatal shooting of 21-year-old Danielle Willard unjustified by West Valley City detectives Shaun Cowley and Kevin Salmon.
Bennion also has worked alongside Bret Rawson, who is representing Salmon and who has called for a candidate to challenge Gill in the 2014 election. Bennion, who is an administrative representative though not an attorney, currently represents officers facing administrative discipline on behalf of the Fraternal Order of Police.
Gill said he is not going to enter the political fracas surrounding his announcement.
"My focus has always been and continues to be doing my job, and I take that very seriously and that privilege has been given to me by the citizens, and they'll let me know if I'm not doing my job," Gill said. "I don't need to apologize for my ethnicity or culture or American citizenship or my professionalism."
He said he stands by his decisions and the integrity of the work he and the investigators in his office and in the West Valley City Police Department did to reach their conclusions.
"These are not political decisions, they are based on the law, and no one is above the law," Gill said. "It is the evidence and the law that guides these decisions."
Some of the candidates running for West Valley City mayor agree that should be the approach to handling a case they called saddening and heart-breaking.
Margaret Peterson said the Willard shooting should not be used for political gain by anyone and that she is "confident Mr. Sim Gill performed his duty with integrity." She also said Bennion owes Gill an apology for his comments.
Ron Bigelow agrees that he doesn't want to use the situation for political gain in an election, saying "we just have to let justice take its course."
Another mayoral candidate, businessman Jeffrey Mackay,a former police officer, praised Gill's work on the case.
"I think Sim Gill followed the evidence that he was given," he said. "I believe Sim Gill followed the rules of evidence."
Don Christensen, another mayoral candidate, said Gill has "a job to do and that is to protect the civil rights of everyone, and he's doing that job." He also said West Valley City police and administration will continue to assist the investigation in any way possible.
Alex Segura, a mayoral hopeful, said it was "kind of shameful" to even bring up Gill's ethnicity.
"I don't believe Sim Gill is a cop hater and I support the district attorney in this matter," Segura said. "Let this process move forward from here."
Candidates Tom Huynh and Karen Lang could not be reached for comment.
Gill's office is now investigating the shooting to determine whether to pursue criminal charges against Cowley and Salmon.
Simultaneous federal, county and internal probes have been launched, the department's Neighborhood Narcotics Unit has been shut down after several instances of mishandled evidence handling were uncovered, and 125 state and federal drug cases emanating from that unit have been dismissed by prosecutors concerned they no longer had a legitimate force of detectives to back up their charges.
The case also lives on in federal court, where Willard's parents filed a wrongful death suit against the city in June.
The controversies are swirling in the midst of a search for a new police chief after the March retirement of longtime West Valley City Police Chief Thayle "Buzz" Nielsen. The search is nearly complete and the announcement of the new leader should be made in the upcoming weeks.
Tribune reporter Pamela Manson contributed to this article.