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 that 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.

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 that race played a role in the shooting. A special prosecutor from Jacksonville charged Zimmerman with second-degree murder; he maintains that the teen ambushed him, and that he acted in self-defense.

Detective Chris Serino told defense attorney Mark O’Mara on Monday that 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 that the officers conducted with Zimmerman the night of Trayvon’s death, the 52-minute interrogation on Feb. 29 was at times tense and antagonistic.

“You wanted to catch him. You wanted to catch the bad guy, the f-----g 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 the f---’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 you have 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 that 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.”