Mark Riccardi is a stuntman and actor that has appeared several times in 24:
In Day 5: 4:00pm-5:00pm, he played a terrorist that attacked Yuri Suvarov's motorcade, but he was cut from the final episode. He appears on the extended version of the motorcade attack on the DVD where he and another goon are seen gunning down two SS Agents (one of whom is played by Chris Gann).
In Day 8: 3:00am-4:00am, he played a CTU security guard who was on duty when Kayla Hassan arrived at CTU in a car fitted an EMP bomb. His character ushered Kayla out of the way while they attempted to defuse the bomb, and then was thrown away from the blast when the bomb detonated. Of the four security guards who were near to the bomb when it detonated, Riccardi's character seemed furthest away, so it is likely he was playing McDermott.