Two of Denver’s police watchdogs tangled today over a report criticizing cops’ ability to investigate their colleagues — and the dispute led to a call for a Department of Justice investigation into the city’s police.

The dispute started when Denver’s outgoing Independent Monitor, Richard Rosenthal, released a scathing report in the morning questioning the ability of the city’s police department to investigate the alleged misdeeds of officers. Later the Manager of Safety, Alex Martinez, held a press conference and suggested that the problem is Rosenthal, not the department’s Internal Affairs Bureau.

Rosenthal’s job is to oversee investigations and make recommendations about discipline to the manager. Martinez has final say in how punishment is meted out.

Martinez said Rosenthal, who is leaving for a job in British Columbia after tomorrow, is unnecessarily bringing suspicion and disrepute to the department. What he leaves behind “in his farewell to Denver raises questions about that individual.”

Told about the comments, Rosenthal called for an investigation into the Denver police department by the U.S. Department of Justice.

“It is unfortunate that the Manager of Safety does not appear to understand the significance of the deficiencies in the Denver Police Department’s Internal Affairs Bureau,” Rosenthal said. “As he is the ultimate decision maker for the Department of Safety, his failure to acknowledge there is even a problem is distressing and evidences a need for outside intervention. It is my opinion that the Department of Justice, Civil Rights Division, needs to open an investigation into the Denver Police Department as the department has established its inability to protect the public from police misconduct, including violations of civil rights.”

Rosenthal’s report said members of the Internal Affairs Bureau, charged with investigating police misconduct, drag their feet in examining the incidents, fail to ask important questions, leave evidence out of their reports and show bias in favor of the officers they investigate, Rosenthal said.

Among his conclusions in the fourth quarter report was that “bias on the part of Internal Affairs Bureau investigators and supervisors has been documented in many cases over the past year.”

“It is the opinion of the Monitor that these cases evidence substantial problems in the way the Denver Police Department is currently policing itself,” Rosenthal wrote.

One case, a claim that an officer lied under oath, is still open almost two years after the department refused to order the officer and another cop to provide personal cell phone records that could prove or disprove the claim. Rosenthal brought the matter to the attention of the Manager of Safety’s office in August, last year. “On January 4, 2012, the Monitor was informed that on December 29, 2011, the Department ordered the officers to provide their cell phone records.” The case remains on hold, and the officers are still on patrol.

In another, an investigator “attempted to explain away the officer’s conduct to the complainant and witnesses and also asked leading and suggestive questions evidencing bias in favor of the subject officer,” the report said.

In another case, Rosenthal wrote that the investigator provided both the officer under investigation and witnesses with inaccurate information.

In that same case, the investigating officers failed to interview all necessary witnesses before interviewing the subject officer.

According to Rosenthal, “This action resulted in inaccurate information being provided to the subject officer during his interview and required that a reinterview … be conducted months later, which potentially impacted his ability to recollect.”

In that case, investigators also “exhibited significant bias in favor of the subject officer.”

In another case, IA refused to ask permission to obtain cell tower records from members of a family who claimed that an officer left them stranded after ordering one of them not to drive because of a lack of insurance. The family members claimed they were stranded for 45 minutes before the officer’s supervisor gave them permission to drive home. The officer claimed “multiple times that the complainants had, in fact, driven away within 5-10 minutes,” the report said.

The cell tower records would likely have established where they were located during the 45-minute period. “At any point in time during the command review process, the department could have requested that the cell tower information be obtained,” Rosenthal wrote.

Martinez said that in none of the cases would any of the information Rosenthal said was missing have changed the outcome. He called the report “nitpickey.”

Rosenthal, who came to Denver in 2005 from Portland, Ore., where he had initiated an independent monitor’s office, is leaving the position at the end of the week to create and head a new independent investigations office in British Columbia.