I've been looking into this for the last couple hours, and best I can tell the basis of this is "they look kinda alike" and screenshots of an anonymous FB messenger conversation. If it is him, here is how you'd prove it... https://twitter.com/dyllyp/status/1266166402521522176

1) ID the clothes, especially shoes. Can you find previous pics of this same guy in them?
2) The respirator is commercial, from Honeywell. Is that issued by the St. Paul/Minneapolis police, or just commercial?
3) Most importantly, find more photos/videos of Umbrella Man.

You'd have to find lots of semi-unique facial details (as he's all covered up elsewhere, and I didn't see a watch or specific jewelry items on him) to make the match. The cop everyone is hounding has a few freckles/moles.
High-res of the Umbrella Man clip:
https://video-ams4-1.xx.fbcdn.net/v/t39.24130-2/10000000_704696513684739_7571916135688204727_n.mp4?_nc_cat=103&_nc_sid=985c63&efg=eyJ2ZW5jb2RlX3RhZyI6Im9lcF9oZCJ9&_nc_ohc=3tgBidh9esQAX8ksAXK&_nc_ht=video-ams4-1.xx&oh=fc77213ae3c00a92d5723d28c6f0cb9c&oe=5EF5E945

There's also a low-res Periscope showing him, but I don't think that gives you much more other than an estimate at his height and maybe a small voice sample. https://www.pscp.tv/w/1ynJOpDZrawxR?t=13m31s

Realistically, unless there is some extremely high-resolution photo or video close up to Umbrella Man's face or this supposed ex from the FB convo comes out, this will just be another story of internet justice gone wrong or forever unresolved.

In the meantime, redirect sleuthing into figuring out who this cop is https://twitter.com/JordanUhl/status/1266193926316228609?s=19