[Spktyr]

There's another picture floating around that purports to be a different example of a similar homemade type, previously found by Japanese police.

Clearly this isn't the same gun, but if the shooter's gun is similar, it might be striker fired.

[riverrunner]

One can clearly see the strikers on this picture.

One can see pipe caps on the one used.

This one looks like a much nicer design.