SANFORD -- Some details in George Zimmerman's account of what happened the night he fatally shot Trayvon Martin changed in his various interviews with investigators, according to testimony Monday in Zimmerman's second-degree murder trial.
But the two lead Sanford police investigators in the case said under cross-examination they did not consider the differences in Zimmerman's statements significant.
"Most people don't tell you the same story the exact same way two times," Officer Doris Singleton testified.
Monday marked the start of the second week of testimony in a case that has drawn national attention in the year and a half since Trayvon, an unarmed 17-year-old from Miami Gardens, was shot and killed in a Sanford gated community while visiting his father.
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A 44-day period between the shooting and Zimmerman's arrest prompted Justice for Trayvon protests and marches in Sanford and in other cities as well as accusations race played a role in the shooting.
A special prosecutor from Jacksonville, taking over the case from Sanford Police, charged Zimmerman with second-degree murder; Zimmerman maintains the teen ambushed him and he acted in self-defense.
Detective Chris Serino told defense attorney Mark O'Mara Monday he and Singleton were under intense pressure to move the case forward.
That pressure is partly what led to what O'Mara called a "challenge" style of interrogation of Zimmerman by
Serino and Singleton three days after the shooting.
In contrast to non-hostile interviews officers conducted with Zimmerman the night of Trayvon's death, the 52-minute interrogation Feb. 29 was at times tense and antagonistic.
"You wanted to catch him. You wanted to catch the bad guy, the punk who can't get away," Serino said to Zimmerman, referring to a phrase Zimmerman used on the phone with a police dispatcher.
One detail that changed from Singleton's initial interview with Zimmerman to a walk-through of the scene the next day followed by the Feb. 29 interrogation was what he remembered Trayvon saying to him.
"He jumped out from the bushes. He said, 'What's your problem, homie?'" Zimmerman, under Miranda warning, said to Singleton in the recording played in court Monday.
"I said, 'I don't have a problem.' He said, 'Now youhave a problem,' and he punched me in the nose. He just started punching me in the face. I started yelling for help."
In a later interview, Zimmerman said the teen's first question was, "You got a problem?"
Last week, a witness from Miami who was on the phone with Trayvon moments before the shooting testified that she heard her friend say, "Why are you following me for?" before the phone cut off.
Serino and Singleton pressed Zimmerman in the interrogation about what he thought Trayvon meant when he asked Zimmerman what his problem was. They suggested Trayvon was "creeped out" and frightened by Zimmerman pursuing him, causing Trayvon to run at one point.
Zimmerman said he couldn't remember how fast or where Trayvon was running.
"I don't understand, George," Serino said in the interrogation. "It's kind of important. It sounds like he's running to get away from you."
Serino said Monday he thought Zimmerman's injuries were "lacking" when compared with his statement Trayvon punched him 25 to 30 times and repeatedly slammed his head against a concrete walkway until Zimmerman said he "felt like it was going to explode."
"I still kept an open mind that he could be a victim," Serino testified.
Serino has called the events that unfolded "avoidable" and recommended manslaughter charges against Zimmerman. The 15-year veteran later told FBI investigators he was pressured by black officers into filing charges and did not believe there was enough evidence to support charges.
That shift in stance could raise questions about the credibility of the law-enforcement witness in the murder trial.
Serino hired lawyer Jose Baez, well-known after his successful representation of Casey Anthony in her 2011 murder trial. Baez, who no longer represents Serino, told NBC's "Today" show Monday that Serino "did exactly what he was told through the course of the investigation, until it became outright political."
A large portion of Monday's hearing consisted of jurors hearing recordings and watching video of Zimmerman's statements to police.
Also Monday, an FBI voice-recognition expert testified it was scientifically impossible to determine whose voice is screaming for help in a 911 recording of the fight and shooting.
Hirotaka Nakasone said he was able to isolate less than three seconds of uninterrupted screams from the 911 call, which he said was not enough for accurate voice comparison.
He did say, however, people familiar with the voices in question may be better able to identify the voices.
Trayvon's parents, who say the screams belong to their son, and Zimmerman's father, who thinks the screams are his son's, are expected to testify at some point.
Miami Herald staff writer David Ovalle contributedto this report.