A part of my campaign is going to focus a lot on tech heresy, specifically the work of Umbra Malygris. I haven't found a lot of info on him or his works so far outside of the dark heresy books. Anyone have any ideas on what kind of stuff he might have made or collected in the Altar of Genocide?

What was he on about, again? I do remember a reference to the Malgyrian Heresy being mentioned in the Calixis timeline.

Bio-Tech-Heresy, among other things, IIRC. Malygrisian (sp?) Bio-forging, talked about in the RH, I believe.

most you'll find anywhere is:

This Explorator Archmagos Umbra Malygris and hundreds of his Adepts went renegade in 742M41 after clashing with the High Fabricator of the Lathes in the Calixis Sector. He unleashed a number of forbidden weapons against seemingly random opponents to further his research and gain secrets from vanquished foes. The Mechanicus Dragon Secutarii destroyed him in 770M41, but his lore still plagues the Mechanicus.

You'll find some references/inspiration in the Radicals handbook, page 122 and 190-192 and also a background package in the Inquisitor's Handbook. IIRC there are a few other mentions in some other books. Probably creatures Anathema and Disciples of the Dark Gods.

Good Luck

Oh yes and further inspiration might be found in any fluff about Fabius Bile and in the 2nd book of the grey knights series from Black Library and possibly in the Dark Creed series