Joe Burbank / AP Prosecutor Bernie de la Rionda, right, demonstrates a possible scenario while questioning state's witness Chris Serino, a Sanford police officer, during the George Zimmerman trial in Seminole circuit court on Tuesday, July 2 in Sanford, Fla.

The lead investigator for George Zimmerman’s case testified on Tuesday that he believes Zimmerman may have exaggerated the manner in which he was injured during the confrontation that resulted in Trayvon Martin’s death last year.

Zimmerman, charged with second-degree murder in the death of the 17-year-old unarmed teenager, has pleaded not guilty, claiming Martin attacked him on Feb. 26, 2012, in the gated Sanford, Fla., community where the two encountered each other. Martin died of a single gunshot wound; Zimmerman was photographed by police that night with a bloody, swollen nose and wounds to the back of the head.

Zimmerman alleges Martin straddled him after punching him in the nose and banged his head repeatedly against the sidewalk, warning him before Zimmerman fired a shot at him, “You’re going to die tonight.”

On Tuesday, Chris Serino, the lead investigator in Zimmerman’s case, took the stand for a second day and testified that based on Zimmerman’s statements following the teen’s death, he felt Zimmerman may have been exaggerating the manner in which he was injured.

“You felt he was exaggerating certain parts of it?” prosecutor Bernie De La Rionda asked Serino.

“Among other things,” Serino said.

“Did you feel he exaggerated the manner in which he was hit?” De La Rionda asked.

“Yes, sir,” Serino responded.

When questioned later during cross-examination, Serino added he believed Zimmerman could have exaggerated the number of times he was punched or hit.

The back-and-forth on the stand followed testimony Monday during which Serino told the court he believed Zimmerman was relieved after being told by investigators last year – falsely – that video may exist of the shooting. Serino had testified on Monday that he tried to bluff Zimmerman about the existence of a video to provoke a reaction and gauge Zimmerman’s assertion that he shot Martin in self-defense.

"The fact that George Zimmerman said to you, 'Thank God. I hope somebody did videotape the event, the whole event.' His statement – what did that indicate to you?" defense attorney Mark O'Mara asked Monday.

"Either he was telling the truth or he was a complete pathological liar. One of the two," Serino responded.

When questioned further, Serino said he thought Zimmerman was telling the truth and was not a pathological liar.

On Tuesday morning, Judge Debra Nelson sided with a demand by prosecutors to strike those remarks as improper testimony, ruling it was beyond O’Mara’s scope to ask someone on the stand to characterize Zimmerman’s state of mind.

Later in the day, Mark Osterman, who describes Zimmerman as the “best friend I’ve ever had,” took the stand. Osterman, who works for the federal air marshal service and has written a book about Zimmerman’s case, said Zimmerman was driving to the supermarket to go buy his lunches for the week like he did every Sunday when he saw Martin on that rainy evening last February.

Osterman went with Shellie Zimmerman, George Zimmerman’s wife, to pick Zimmerman up from the Sanford police station the night Martin was killed, and described Zimmerman’s account of the how their confrontation began to the court.

“He observed Trayvon walking between two sets of townhomes and looking into, I believe there was a window to one where the light was on and you could see that someone was looking into the window of a townhome. And it was about that time that Trayvon and George made eye contact with each other and both aware of the other’s presence,” Osterman told defense attorney O’Mara.

Zimmerman then called a non-emergency police line to report a suspicious person, following Martin despite non-emergency personnel saying it wasn’t necessary for him to do so, Osterman said.

Osterman testified that Zimmerman told him Martin then allegedly said to Zimmerman, “’Do you have a problem,’ and then he used a curse word,” and their confrontation began. Martin allegedly reached for Zimmerman’s gun during the encounter, according to Osterman’s re-telling of Zimmerman’s account, and Zimmerman knocked Martin’s hand away from the gun while the two brawled.

Editor's note: George Zimmerman has sued NBC Universal for defamation. The company strongly denies the allegation.

Related content: