The killings were higher where Tutsi and Hutu intermingled (11%) but there was still killings in a Hutu only area (5%).  

I find this most persuasive:

The percentage of the population consuming less than 1,600 calories per day (i.e., what is considered below the famine level) was 9% in 1982, 40% in 1990, and some unknown higher percentage thereafter.

People were starving to death in the midst of agriculturally productive land.  They didn't have enough land to grow enough food.  There were two options:  

1.  Starve
   
2.  Obtain more land

Similar situation occurred in the Sudan, there the trigger was lack of water and is starting to happen in Kenya.  Countries based on subsistence agriculture have a minimum acre/family farm size.  As the average farm falls below that figure tensions, primarily ethnic tho' also generational, sibling rivalry, economic class, and political tensions also increase.  Please note the last two.  By definition political tension is a threat to the Ruling Elite and, thus, provides the stimulus for a faction of that elite to continence and support intra-country violence.  The Ruling Elite, having the ability to organize and orchestrate violence does remain the immediate, proximate, trigger but the cause was per-capita food consumption.

She believed in nothing; only her skepticism kept her from being an atheist. -- Jean-Paul Sartre