SPOKANE, Wash. (AP) — The man charged with planting a bomb along the route of the Martin Luther King Jr. Day parade in Spokane pleaded not guilty on Monday to the four charges against him, including new hate crimes charges.

Kevin Harpham, 36, entered the pleas before U.S. Magistrate Cynthia Imbrogno. Harpham, who has extensive ties to white supremacist groups, remains without bail in the Spokane County Jail.

Public defender Roger Peven said afterward that the additional charges of a committing a hate crime and using a firearm during a violent hate crime — which carries a minimum sentence of 30 years — raise the stakes for his client.

“This is very serious,” Peven said. But two of the charges also carry maximum sentences of life, and “that’s kind of high, too,” Peven said.

Harpham replied only to the magistrate’s questions during the brief court appearance. Trial is set for May 31 in federal court. The bomb was found the morning of Jan. 17 and was disabled before it could explode.

Assistant U.S. Attorney Tom Rice could not say if any more indictments are anticipated in the case.

Harpham last month pleaded not guilty to attempted use of a weapon of mass destruction and unauthorized possession of an unregistered explosive device. A grand jury this month added the two additional charges. The superseding indictment contended Harpham planted the device in advance of the Spokane parade “because of actual or perceived race, color and national origin” of participants.

Legally, the bomb is considered a firearm, Peven said.

The Hate Crimes Prevention Act was passed by Congress in 2009, and this is its first use in the Eastern District of Washington, Peven said. This will be his first defense of a client charged with a hate crime, he said.

Despite the charges, little about the motivations in the case are known because federal prosecutors have been granted their request to seal court documents about the investigation that led authorities to arrest Harpham on March 9.

Prosecutors contend releasing details would hamper an on-going investigation, and could taint the jury pool.

The Associated Press, Cowles Publishing Co., and The Seattle Times have argued that the documents should be released because Harpham is in jail. However, U.S. District Court Judge Justin Quackenbush ruled last week that Harpham’s right to a fair trial outweighs the media’s right to the documents. He also ruled that the press does not traditionally have the right to see search warrant and grand jury materials.

The Southern Poverty Law Center, which tracks hate groups, has said that Harpham made more than 1,000 postings on an Internet site used by racists called the Vanguard News Network. The SPLC has also said that Harpham belonged to a neo-Nazi group called the National Alliance.

His father, Cecil Harpham, has said his son talked to racists on the Internet regularly, but never acted on racial hate.

Kevin Harpham lived on 10 acres near Addy in rural Stevens County, 50 miles north of Spokane.

Copyright 2011 The Associated Press.