DENVER -- The U.S Attorney's office on Thursday denied the request of Columbine families to hold a federal grand jury to investigate the shootings.

"The most credible evidence available, including compelling statements from several students who witnessed the events, indicates that Daniel Rohrbough was killed by Eric Harris and Dylan Klebold," U.S. Attorney John Suthers said in a press release.

In lawsuits and interviews, victims' families have accused authorities of ignoring warning signs, responding too slowly to the attack and mishandling the investigation.

Investigators in Jefferson County insist that they did the absolute best they could under the circumstances.

The family of Danny Rohrbough had said publicly that they wanted a federal grand jury and/or a legislative committee with subpoena powers to look into the death of their son.

They said that the evidence they have show that Denver SWAT Officer Dan O'Shea killed their son, and not teen gunmen Harris or Klebold.

But in Thursday's rejection of the request, Suthers said, "The only legitimate use of a federal grand jury is to determine whether there is probable cause to believe a federal crime has been committed. It is not appropriate to use such a body to investigate a matter simply to get to the bottom of it."

Harris and Dylan Klebold killed 13 people and wounded 23 other people before killing themselves on April 20, 1999.

A legislative committee to look into the police investigation of the crime is currently being considered in the Colorado House of Representatives. It would require people to speak who have declined to do so because of litigation.