Did some digging, turns out the Pegasus Museum building was at one point a DIY music venue called Paper Sun. Here's a Facebook local business page. Last post from 2014 and appears to be closed.

"If it wasn’t for the telltale black balloons hanging outside a Columbia Heights alleyway, you might not have been able to find Paper Sun — a two-story warehouse/art space where local bands practice and sometimes even play intimate shows. The cloistered garage provides a great off-the-beaten path venue away from crowded bars like Wonderland Ballroom, and great acoustics." Source

I found these by looking at the Flickr gallery of photographer Chris Chen (Fur Cafe).

He has a Flickr gallery called Rock & Roll Flea @ Paper Sun from July 2013 which includes this photo of three hipster looking folks standing outside the building we now refer to as the Pegasus Museum.

And this photo of two women sitting next to a garage that appears to be the same garage doors across the street from Pegasus.

This photo looking down stairs toward a doorway appears to be the same door that the woman was coming out of in the other photo. You can tell by the cracks on the concrete outside.

This leads me to believe that the rest of the pics at Rock & Roll Flea were from upstairs. The event itself looks like a punk rock flea market with artists, music, etc. Nothing suspicious with that.

But...

This gives an idea of what the upstairs of the Pegasus building looked like in 2013.

Video of a band performing at Paper Sun - Looks like it was on the first floor, rough brick walls. Same room as "kill room"?

More photos tagged "Paper Sun" on Flickr

THIS PHOTO has the same "tree trunk" table that we saw in the Joe Corbin Wills photos. It was taken from above, in what I assume to be from that mysterious 2nd story doorway.

This photo from 2010 of folks standing outside the door

When did JA buy the building and start renovating it? What ever happened to Paper Sun? Why did it close?

Edit: formatting