When Jack Bauer was undercover with terrorists at the Sunrise Hills Shopping Mall, Curtis Manning organized CTU backup including Walsh and Michaels. They waited outside the mall until Sentox gas was released, after which Bill Buchanan ordered the teams to move in. Curtis ordered them to inject any casualties to help them live, but Jack informed him that a hostile had escaped. After ordering Michaels to stay at the mall, Curtis then told Walsh to bring his team with them in the pursuit of the hostile.
Walsh and his team followed the terrorist to 1136 East Muldower. However, after donning gas masks and raiding the building they found the hostile had taken his own life to avoid capture. CTU then realized their only link to the terrorists was gone. ("2:00pm-3:00pm")
Background information and notes
A group of agents respond to Curtis's order to Walsh and his team, but it is not specified which one of them is Walsh.