A report of an FBI interview with the lead detective investigating the shooting death of Trayvon Martin suggests that within the Sanford police department, the question of whether to arrest  George Zimmerman for the killing broke down along racial lines.

Investigator Chris Serino, who interviewed Zimmerman multiple times and ultimately filed a “capias” request suggesting manslaughter charges against Zimmerman, wrote in that request that his investigation concluded that Zimmerman followed Martin, 17, on the evening of February 26th because he “reached a faulty conclusion as to Martin’s purpose for being in the neighborhood” where Zimmerman and his wife rented a townhome. The capias was filed with the Seminole County State Attorney on March 13th.

The day before, police chief Bill Lee held a press conference in which he insisted that the department lacked probable cause to arrest Zimmerman. Then on March 16th, the same day the city released 911 calls from neighbors on the night of the shooting, Lee and Serino sat down with a local newspaper and insisted that not only did they lack cause to arrest Zimmerman, but they would have violated his constitutional rights under Florida’s Stand Your Ground law had they arrested him for shooting Martin to death.

What changed in the 24 hours between the department’s official stance that there was no evidence Zimmerman committed a crime, and the filing of that capias the next day has been an ongoing question in the case. Now, a report of an interview that federal investigators conducted with Serino nearly a month after the filing sheds new light on what Serino believed was at work.

In an April 3rd interview with FBI investigators (incorrectly dated March 3rd in the filing, which was released by prosecutors on Friday as part of a new round of discovery in the case against Zimmerman), Serino alluded to pressure from within the department to file charges in the Martin shooting, and a concern that leaks to the public were inflaming the case. Protests in Sanford, weeks after the shooting, ultimately led to Lee stepping aside as police chief. He was fired from the department formally last month. The case ratcheted up racial tensions in Sanford, but also within the Sanford police department, which was no stranger to racial conflict, both with the community and within its ranks.

“Serino is concerned that many of the leaks in this case are coming from within the Sanford Police Department,” the FBI report states. Serino reportedly named the officers he believed were behind the leaks: officers Arthur Barnes, Trekell Perkins and Rebecca Villalona. Barnes and Perkins are black. Villalona is white, but is married to an African-American. Serino is Cuban-American.

Perkins is the officer who took the statement of Witness 9, a woman who claimed to know Zimmerman and his family, and who accused Zimmerman of being racist, and “hating black people.” Neither Villalona nor Barnes were involved in the Zimmerman investigation.

Barnes, a 25-year veteran of the police department and a Sanford native, was himself interviewed by FBI agents on April 5th. The former Army M.P., who was assigned to the property crimes division, talked to the investigators about the racial makeup of Sanford, and told them “the number one crime issue in the City of Sanford is burglaries,” including for his division. The Retreat at Twin Lakes subdivision, where Zimmerman and his wife rented a townhouse, had seen nearly a half dozen break-ins in the year prior to the Martin killing, and Zimmerman himself had called in several “suspicious person” reports, all involving young black males, on August 3 and 4, on October 6, 2011, and again on  February 2nd. The Twitter account for the Retreat at Twin Lakes homeowner association boasted on February 12th about the success of their neighborhood watch program, for which Zimmerman — though a renter, not a homeowner — was the coordinator.

Barnes told investigators that while he was “unsure how the younger African-American community” would react to the outcome of the investigation, he believed “the African-American community would be in an ‘uproar’ if Zimmerman” was not charged. “The community will be satisfied if an arrest takes place,” the report of two FBI agents states. “As for the civil rights investigation, if it is determined to be a violation of Trayvon Martin’s civil rights then it will reflect negatively on the Sanford Police Department and fingers will be pointed at them for not doing their job properly,” the report states, adding that Barnes believed the community was split “50/50″ on whether the shooting was a hate crime, but that he did not believe the shooting was racially motivated. “It was a man shooting an unarmed kid,” the report states Barnes told the FBI investigators.