For weeks, a jury has heard testimony prosecutors say proves James Wells is guilty in the fatal shootings of two Coast Guard colleagues in Kodiak two years ago. On Day 11 of the trial, Wells' defense began introducing witnesses to refute that accusation.

Wells' physician, Dr. Song-Quin Gan, first took the stand to describe his medical history. She said for years Wells suffered from chronic diarrhea as a side effect from medication he took to treat diabetes.

Wells' attorney says on the morning of April 12, 2012 -- the day when Coast Guard Electrician's Mate First Class James Hopkins and retired Chief Boatswain's Mate Richard Belisle were shot -- his client was in a bathroom for nearly 25 minutes, before returning home to fix a flat tire on his truck.

Under cross-examination by the prosecution, Gan said she reported Wells was fine after his last checkup, and that she didn't note any gastrointestinal issues he was having.

The second defense witness on the stand Thursday, Michael DiTallo, is an expert hired to analyze work done by the prosecution's expert witness on car identification. DiTallo reviewed surveillance video from a Coast Guard building near where Hopkins and Belisle were killed, which shows a blue vehicle approaching and then departing the area.

The prosecution says the vehicle seen is most likely a blue Honda CR-V, the same car Wells' wife owns.

DiTallo explained that even more vehicles fit the shape and size of the one seen in the video than the four SUVs the prosecution's expert testified to. DiTallo compared the vehicle outline to eight different vehicles.

"In your professional opinion, the vehicle we saw could be any of those vehicles?" a defense lawyer asked.

"Yes, and there could be others," DiTallo answered.

Wells' defense will continue to bring forward witnesses for the next few days, but hasn't announced whether he will take the stand in his own defense.