Suspected Kirk Shooter’s Gaming History Probed by Secret Service

Suspected Charlie Kirk shooter Tyler Robinson used Donald Trump’s name as a pseudonym on Valve Corp.’s Steam video-game platform, a fact that’s become part of a profile US law enforcement is building on the alleged assailant.

The US Secret Service has joined the investigation into the shooting, even though Kirk wasn’t under the agency’s protection, according to people with knowledge of the matter.

Agents are working with the FBI to study Robinson’s behavior and online activity, including his use of Trump’s name on Steam, as part of a profile they are building, according to one of the people, ...