if you go to wikipedia.org and search for clone commandos or you find a part where it says that gamma squad was sent onto kasyyyk to find sev but failed. they were forced to retreat losing 3 commandoes in the process.
Drectly from Wikipedia:
"Gamma Squad was the only known team to have serious defects. A Kaminoan made a series of mistakes and altered them all in very significant ways. The aggression level of one was boosted by a factor of ten. Another was mistaken for an ARC trooper and changed to those standards, and the intelligence of a third was also boosted by a factor of ten. The fourth member was fixed before it was too developed for the changes be reversed. The Squad went on to several successful campaigns at Geonosis, Byss, and Felucia. The Squad's last battle as a team was on Kashyyyk. Their objectives were
1. Follow Delta Squad 2. Regroup with Delta
The were cut off several times by Trandoshans and droids, and were unable to regroup with Delta. They arrived at the Gun area when they got the disturbing news about Sev and were given one final Order.
They failed to even find him with scanners. They were soon surrounded and were forced to retreat without Fiver, AJ, and Ripper. 3 hours after that they were declared KIA. The rest of the Squad continued to missions on Coruscant during the battle there. During the battle of Coruscant, Sarge was killed in a Fatal explosion. Semper was surrounded and also killed. After the death of Semper and Sarge. Arctic, Sean, Flippy & Parker were sent to the Jedi Temple to assassinate Captain Jaller Obrim. when they failed they were sentenced to death. Darth Vader attempted this, but was injured by a Flash bang thrown by Arctic. After that nobody knew the whereabouts of Gamma."