Two students were killed Tuesday morning at Marshall County High School when a 15-year-old classmate opened fire. The boy will be charged with murder and attempted murder. (Jan. 23) AP

LOUISVILLE — The school shooting in Kentucky’s Marshall County on Tuesday morning took Christina Hadley Ellegood’s breath away.

Twenty years and one month ago, her younger sister, Nicole, was one of three students killed at Heath High School in Paducah, Ky., when 14-year-old Michael Carneal opened fire on students standing in a prayer circle.

“I couldn’t believe this could happen to our small community again,” said Ellegood, 36, a paralegal in Paducah. “I was totally shocked. I told my boss it had to be a joke.”

Ellegood, who helped raise money to erect a memorial to the Heath victims last month, said she has reached out to those responding to Tuesday’s shooting to offer her help.

“I have people from Heath on standby,” she said. “We know what these people are going through more than anyone.”

On Dec. 1, 1997, Carneal wrapped a shotgun and a rifle in a blanket and took them to school, passing them off as an art project. He also carried a…