Targeting girls, they could have poor relationships with women resulting in a feeling of revenge on the girls. The servant/slave aspect could be targeting black women as he's racist or because they're considered weaker and they can't fight back as easily (as slaves), or it's because people wouldn't care as much about them as they're only slaves. Murders = multiple cases, not feeling relieved from just one, likely pointing to mental illness. The Texan part likely just means he lives nearby.
Sorry if this doesn't help! I tried to just use common logic here ^^