Jesse Van Rootselaar, 18, created the virtual “experience” on the online gaming platform Roblox before his terrifying real-life rampage, a rep for the company confirmed.

Mappa continues to elevate Gege Akutami's megapopular manga with kinetic key animation and, more importantly, its painterly scripts.

Roblox is a platform that has thousands of individual experiences and games, many of which feature Roblox codes. Developers ...