arm and i grabbed my gun and i aimed it at him and fired one shot. >> reporter: dna testing seems to agree. there was no trace of trayvon martin's dna on the gun's grip. prosecutors list osterman's book with zimmerman's conflicting account as potential evidence, possibly to challenge zimmerman's credibility. as for his connection to the gun zimmerman was carrying, osterman says it's hard to answer the question does he feel regret. >> so, i would wish it would have never happened. however, the reason why george had it, it was not for malice. he didn't have it to go out and commit a crime of hunting someone down and harming them. it was for self protection. and i'm glad that that firearm was used to protect george. >> and now david, so, if he really is george zimmerman's best friend, how does mark feel about, at this point, you're