DUBLIN, Calif. -- Michael Alexander Allan has admitted to participating in the theft of about 200 pounds of explosives from a San Mateo County facility over July Fourth weekend, according to a criminal complaint filed against him Friday.

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Bureau of Alcohol, Tobacco, Firearms and Explosives special agent Kenneth Kwak said in an affidavit that after Allan was arrested in Union City early Thursday morning, he "proceeded to give a lengthy, detailed statement in which he admitted that he participated in stealing the explosive materials from the location in San Mateo County and possessing them in the van outside of which he was arrested."

Kwak's affidavit indicates that Allan, 46, who has no known address, may have had an accomplice.

The affidavit says that a woman friend who was with Allan when he was arrested told authorities that on July 4 she observed Allan and "a person unknown to her except for the first name of 'Dean'" moving items, including what she believed to be hand grenades, into storage lockers in Hayward that she and Allan share.

The woman, identified in court papers only as "Carter," later saw Allan and "Dean" move most of the explosives materials to a storage locker located near Hegenberger Road and the Oakland Coliseum, according to the affidavit.

Dressed in white jail clothes and sporting a goatee, Allan, an-ex-felon who has no known address, appeared in federal court in Oakland on two charges stemming from the theft of the explosives.

Allan listened quietly as U.S. District Court Magistrate Judge Wayne Brazil told him that he is charged with knowingly possessing explosive devices and materials that had moved in interstate commerce and that he knew or thought that they were stolen.

Some of the materials came from the Louisiana Ordinance Plant, according to the affidavit.

Brazil told Allan that he also is charged with being an ex-felon who possessed explosive devices that moved across state lines. The judge said Allan faces total maximum penalties of 20 years in federal prison and $500,000 in fines.

In addition, Brazil told Allan that, based on the information in the affidavit, not to be surprised if he's also charged with stealing explosives.

Allan, who is being represented by a federal public defender, is scheduled to return to court July 14 for a bail hearing.

According to the criminal complaint against Allan, he has three prior felony convictions: two for taking a vehicle without the owner's consent and one for second-degree burglary.

Records indicate that he was placed on five years' probation in May 2001 for the second-degree burglary conviction and then placed on three years' probation last November for a misdemeanor conviction for trespassing.

The explosives were taken, in a theft discovered over the weekend, from a storage bunker near Crystal Springs Reservoir that houses five explosives magazines used by the San Francisco Police Department, the San Mateo County Sheriff's office and the Federal Bureau of Investigation.

Allan was arrested early Thursday morning after authorities received a tip. They found some of the missing explosives in a van he was driving and other explosives in a storage locker in Hayward.

The materials included electric and non-electric blasting caps, various types of detonator cord, smokeless powder, grenades and grenade-type devices, assorted ammunition, binary explosives, and C-4 military explosives.

According to the affidavit, the woman friend identified as "Carter" has been "acquaintances" with Allan for 10 years. The woman said she owns two storage lockers at the Jackson Street Mini Storage at 77 Traynor St. in Hayward and she allows Allan to store property there.

After reading about the explosives theft in a local newspaper on July 7, the woman realized that the items stored in her locker probably related to that theft so she contacted Allan by telephone and told him they needed to talk in person, according to the affidavit.

The woman said she met Allan in the Food Max parking lot in Union City Wednesday night to confront him about the explosives and tell him to move the items out of her storage lockers, the affidavit says.

Kwak said in the affidavit that authorities first arrested Allan for possession of a stolen license plate, which was affixed to the van he was driving.