Robin Westman — the Minnesota catholic school mass shooter — asked security guards at the dispensary where he worked about guns prior to his murderous attack — and was also obsessed with playing super violent video games … TMZ has learned.

A former coworker of Robin’s at a Rise medical cannabis dispensary tells TMZ … Robin started with the company in late March, and the two worked together up until a week before the shooting — but Robin never really let on about the deadly plan, yet there were signs.

Our source says although they never heard Robin bring up guns at work … one coworker told them in the aftermath of the shooting that Westman asked the security team about firearms, though it was not clear in what context.

On one occasion — during a group discussion on religion — we’re told Robin said organized religion was bad, and it corrupted people. Our source says Robin once mentioned they didn’t like President Donald Trump, but didn’t talk about politics much.

And get this … We’re told Robin would write quite a bit in a journal at work — and even when the staff went out for social events. But, our source says, the staff didn’t know what Robin was scribbling and didn’t pay it much mind until police found Westman’s manifesto.

In the manifesto, Westman offers thoughts about killing President Trump and seems fascinated with school shooters. Robin also included photos of gun cartridges with racial and antisemitic messages written on them, as well as an image of a shooting target over Jesus Christ.

However, our source also tells us … Robin was kind and funny at work … and never threatened anyone or got into a physical altercation.