An unemployed software consultant pleaded not guilty to running a bomb factory at his home, where prosecutors said they found the largest amount of certain homemade explosives in one location in U.S. history.

The San Diego Union-Tribune and North County Times reported that George Djura Jakubec, 54, entered pleas Monday in San Diego County Superior Court to 28 charges, mostly involving possession or manufacture of explosives. Jakubec also was charged with robbing two banks.

It was unclear what Jakubec intended to do with the explosives and weapons, Deputy District Attorney Terri Perez said.

The explosives were discovered last week when a gardener was injured in a blast that occurred when he stepped on explosive powder in the backyard. Mario Garcia, 49, suffered eye, chest and arm injuries and was recovering.

Bail was set at $5 million during the arraignment of Jakubec at the Vista courthouse. A call by The Associated Press to Jakubec's public defender Lacey Martz was not immediately returned Tuesday.

Judge Marshall Hockett said the defendant was an extreme danger to the community and a flight risk because he frequently visited Mexico, the North County Times reported.

Jakubec remained jailed Tuesday. He could face up to 40 years in prison if convicted.

Authorities said they found at least nine pounds of dangerous materials at his rented Escondido home. The chemicals have been used by suicide bombers and insurgents in Iraq and Afghanistan.

The materials include Pentaerythritol tetranitrate, or PETN, which was used in the 2001 airliner shoe-bombing attempt as well as in last month's airplane cargo bombs, prosecutors said.

The other chemicals were highly unstable Hexamethylene triperoxide diamine, or HMTD, and Erythritol tetranitrate, or ETN, authorities said.

Perez called it the "largest quantity of this type of homemade explosives found in one location in the history of the United States."

Authorities also said they found 13 uncompleted shrapnel-wrapped grenades.

Some lanes of nearby Interstate 15 was closed for several hours last week while a bomb squad blew up some of the materials.

Jakubec was on probation after pleading guilty to a burglary charge stemming from shoplifting at an electronics store last year, court records show.

While unemployed for three years, Jakubec became increasingly obsessive, his recently separated wife, Marina Ivanova, told the Union-Tribune.

"I am afraid for my husband's mental state," she said. "He's not well."

She said Jakubec bought chemicals and electronics with money she earned from her job, but she did not know the purpose, she said.

District attorney spokesman Steve Walker said the charges include 13 counts of possession of a destructive device, 13 counts of possession of ingredients to make a destructive device, and two counts of robbery. Prosecutors also filed a special allegation of great bodily injury that could enhance a possible sentence.