SPOKANE, Wash. -

Federal magistrate Cynthia Imbrogno told MLK Day bomb suspect Kevin Harpham Wednesday he faced up to life in prison if convicted of trying to use a weapon of mass destruction in court.

A pair of not guilty pleas were entered on Harpham?s behalf during his arraignment Wednesday, a day after a grand jury determined the government had enough evidence to charge him with attempting to use a weapon of mass destruction and being in possession of an unregistered improvised explosive device.

Kevin Harpham appeared in U.S. District Court wearing a jail-issued tan jump suit. During the arraignment he was told he had been indicted by a federal grand jury of his peers, formal charges Harpham's public defender doesn't take lightly.

?Well any time the grand jury indicts that's an indication of the seriousness of the evidence against someone. It's not an indication of guilt but yes it's serious,? federal public defender Roger Peven said.

Magistrate Imbrogno asked Harpham if she could enter not guilty pleas on his behalf. Harpham repeated not guilty but along with his attorney doesn't know the strength of the case against him.

That?s in part because there?s no word yet on what evidence was presented to the grand jury. U.S. Attorney Mike Ormsby insists this is an active, ongoing investigation that could involve additional charges or suspects. Ormsby is also keeping his case sealed as he?s worried about the potential to prejudice the jury pool.

?I always assume good intentions, and I'm sure it's a desire for a fair trial, along with whatever other interests they have they don't share,? Peven said.

Assistant U.S. Attorney Joe Herrington asked the court to continue to hold Harpham without bond pending his trial. Harpham's defense team says they can't argue for his release until they know more about the case.

?Until we know more about this case that is a problematic issue. We'll wait and see what we have. There are other things more important than that right now,? Peven said.

Meanwhile the investigation is ongoing and investigators say they're surprised they keep turning up new leads that need to be pursued.

Harpham's trial date has been set for May 31.