Lewis said he couldn't discuss the investigation in further detail, including how the couple died and whether authorities believe their deaths are linked to the Jan. 31 fatal shooting of Mark Hasse, an assistant Kaufman County district attorney.

NPR: Texas District Attorney, Wife Found Dead At Home

Nor are they sure whether the deaths are related to the killing of Kaufman County Assistant District Attorney Mark Hasse, who was killed on his way to work in January.

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The slayings came less than two weeks after Colorado's prison chief was shot to death at his front door, apparently by an ex-convict, and a couple of months after Kaufman County Assistant District Attorney Mark Hasse was killed in a parking lot a block from his courthouse office.

NPR: Texas DA Slain In His Home; Had Armed Himself

Mark Hasse, an assistant district attorney in Kaufman County, was shot to death while getting out of his car Thursday morning, sheriff's spokeswoman Pat Laney told CNN.

CNN: Prosecutor gunned down outside Texas courthouse