My bet is it is someone in the military, probably familiar with IED’s, other explosives and devices who has access to these devices and had a relative killed by drug dealers.
Now he is seeking revenge. The three people killed so far are connected by a drug gang.
Texas has numerous bases so it would have to be one that houses explosives and other ordnance.
I haven’t heard that all three victims are somehow related to drug gangs. There was some early police speculation that the first victim might have been mistakenly targeted because he lived near a similar-looking house where a recent drug raid had occurred, but I haven’t heard anything about the other victims having any connection - real or mistaken - to drug gangs.