(CNN) -- The George Zimmerman investigation was hijacked "in a number of ways" by outside forces, said the former police chief of Sanford, Florida.
Bill Lee, who testified Monday in Zimmerman's second-degree murder trial, told CNN's George Howell in an exclusive interview that he felt pressure from city officials to arrest Zimmerman to placate the public rather than as a matter of justice.
"It was (relayed) to me that they just wanted an arrest. They didn't care if it got dismissed later," he said. "You don't do that."
When Sanford police arrived on the scene on February 26, 2012, after Zimmerman fatally shot unarmed 17-year-old Trayvon Martin, they conducted a "sound" investigation, and the evidence provided no probable cause to arrest Zimmerman at the scene, he said.
It had nothing to do with Florida's controversial "Stand Your Ground" law, he said; from an investigative standpoint, it was purely a matter of self-defense.
Zimmerman told police he killed Martin after the teen attacked him. While the evidence at the time corroborated that claim, the ex-chief said, Lee's lead investigator made a recommendation that Zimmerman be charged with manslaughter.
It was a matter of protocol, Lee said. Arresting Zimmerman based on the evidence at hand would have been a violation of Zimmerman's Fourth Amendment rights, he said. Thus, the Sanford police presented a "capias request" to the state's attorney, asking that the prosecutor determine whether it was a "justifiable homicide," issue a warrant for arrest or present the case to a grand jury.
"The police department needed to do a job, and there was some influence -- outside influence and inside influence -- that forced a change in the course of the normal criminal justice process," Lee said. "With all the influence and the protests and petitions for an arrest, you still have to uphold your oath."
"That investigation was taken away from us. We weren't able to complete it," he said.
The Sanford police intended to release the tapes once the probe was over, Lee said, because you can't publicize evidence amid an investigation.
Instead, the mayor told him on March 16 the tapes had been released to Martin's family and the public. The family was asked to help identify voices, Lee said, but if police were in charge of the investigation, they wouldn't have presented evidence to a group.
"It should be done individually so there's no influence on the other people in the room," he said. "Then, there's no questions that can be brought up about how (an identification) was obtained or whether it was influenced."
Releasing the evidence to the public was problematic, as well, because it created the potential for someone to concoct a "story about what they observed when they really didn't observe it," he said.
Martin family attorney Jasmine Rand said she doesn't believe playing the tapes to a room full of people "makes any difference to the outcome of the case."
"We have to remember that that was played for the family in a private room because they were hearing the last moments of their son's life as he cried for help," Rand told CNN's Erin Burnett on Wednesday night. "And I think Sybrina Fulton (Martin's mother) got up and walked out of that room. She didn't sit in there and talk to everybody, because she had a visceral reaction when she heard her son yell for help and she couldn't help him because she knew he was dead."
Lee was placed on paid leave March 22, 2012, after the Sanford City Commission expressed a lack of confidence in him. The same commission rejected his resignation in a 3-2 vote a month later, with dissenting commissioners questioning the fairness of Lee's losing his job.
Two months later, Lee was sacked. City Manager Norton Bonaparte said in a news release, "The police chief needs to have the trust and respect of the elected officials and the confidence of the entire community."
Lee believes lack of confidence did play a role in his dismissal, he told CNN, but he also believes Bonaparte faced political pressure and terminated him "without cause," which was permitted under his employment contract.
"I upheld my oath," Lee said. "I'm happy that at the end of the day I can walk away with my integrity."
Asked whether he would do things differently given the opportunity, the 30-year veteran of law enforcement said there always are things he could change in hindsight, but he stands by the investigation.
At every turn in the 40-minute interview with CNN's Howell, Lee doggedly defended his investigators, saying race never played a role in any decision and that his officers "conducted an unbiased review."
Investigators knew letting Zimmerman walk free for 46 days was an unpopular decision -- and they took abuse for it -- "but they performed professionally. That's the mark of a strong police department."
Lee took issue with the media casting his department as apathetic or lackadaisical in the case.
"A lot of the information that was given out as fact was misinformation," he said. "It was reported in some media that we didn't conduct an investigation for two weeks, but yet in that same media they would show a photograph of a crime scene with crime scene tape, with patrol cars and blue lights and investigators on the scene."
Lee shrugged off the notion that he was hired to clean up racism and other problems in the department. His goal upon becoming chief was to improve professionalism and trust, and he set several goals, all of which were met during his 10-month tenure, he said.
One of his greatest regrets, he said, is that the Zimmerman investigation ultimately shattered his childhood dream to be police chief of the community where he was raised.
"It's a dream of a vision that is going to be unrealized," he said. "I'm at peace with it on most days. I'm a man of faith. But it stings.