District Attorney Mike McLelland and his wife Cynthia were killed on Saturday in their home.
Hours before a memorial service for a Texas district attorney and his wife who were brutally gunned down in their home over the weekend, Gov. Rick Perry announced his office was doubling the reward for information leading to the arrest of their killer from $100,000 to $200,000.
The governor refused to comment on any leads investigators might be pursuing into the deaths of Kaufman County District Attorney Mike McLelland and his wife Cynthia. Speculation has ranged from a lone gunman with a grudge to drug cartels to skinhead gangs; a federal source told NBC News, however, that no theory stands out.
"It is very premature to make any statements about who may or may not have been involved with this," Perry said. "We know we have a porous border. We know that the drug cartels, the gangs, both transnational and otherwise, in some cases, are operating together. So, all of that is obviously open for interpretation and investigation. We will leave no stone unturned."
The McLellands' slayings came three months after the death of Assistant District Attorney Mark Hasse, who was killed by gunshot in broad daylight on Jan. 31 in the town square. Mike McLelland had publicly promised to find Hasse's killer, who still hasn't been caught.
Between those murders, Colorado's prison director, Tom Clements, was shot to death at his house.
A white supremacist parolee who was later killed in a Texas shootout was the main suspect in Clements' death. Kaufman County authorities have not named any suspects in the McLellands' killings.
No apparent connection between the two incidents has been revealed. Bruce Wood, a Kaufman County Judge, said in Thursday's news conference that these are "trying times -- uncharted waters for Kaufman County."
NBC News' Pete Williams and Jeff Black contributed to this report.