He appeared in the 1965 "Gunsmoke" episode "Twenty Miles from Dodge". O'Loughlin played a tough but not insensitive gang leader of stagecoach robbers holding the passengers as hostages for ransom. Among them was Kitty (Amanda Blake) who plays her usual tough-as-nails saloon-keeper, who comforts the freezing and hungry, while battling the desperadoes and a feisty, crafty fellow passenger played by Darren McGavin. O'Loughlin manages to get his hands on the loot, $62,000 & change, but is thwarted by the ingenious explosion of bullets collected round-about by McGavin. This is one of the more grueling and compelling episodes of this western, featuring a strong ensemble cast alongside James Arness, displaying the relentless Marshal Matt Dillon, and aided by the ever-jawin' Festus, Ken Curtis. Sixteen years later, O'Loughlin reunited with Arness in the made-for-TV film "McClain's Law", structured as the pilot for Arness' 1981–82 police detective series.