A convicted felon who lost part of his left middle finger when a homemade bomb exploded in his Alfred home is expected to plead guilty to federal charges that could send him to prison for more than 45 years.

Robert Infante, 47, is charged with weapons and drug offenses and will face a minimum 15-year sentence if he is convicted of being an armed career criminal.

Infante was injured while working in the basement of his home at 60 Avery Way in Alfred on June 25, 2010.

He called 911 and said that a small propane tank had exploded and he needed an ambulance, according to court papers. He got tired of waiting and started to drive himself to the hospital, cradling his bleeding left hand in a T-shirt. He made sure to lock his house behind him.

Infante eventually pulled over on Gove Road and allowed rescue workers to treat his hand in an ambulance before he continued on his own to Southern Maine Medical Center in Biddeford.

Meanwhile, firefighters searched in his house for the site of the explosion, to determine whether there was any more danger. They reportedly found a dozen pipe bombs and materials for making more, as well as 200 marijuana plants.

The firefighters notified state authorities, who worked with the federal Bureau of Alcohol, Tobacco, Firearms and Explosives to obtain a search warrant. A more thorough search turned up two handguns and the .40-caliber and .22-caliber ammunition to go with them.

At the hospital, authorities evacuated the area near the parking lot while they investigated and disposed of a device that had been seen in the back of Infante’s car. Police say they seized five pipe bombs from the car.

Inside, state Fire Marshal’s Office investigator Dan Young was questioning Infante, who was being readied for surgery.

Infante was later charged in U.S. District Court in Portland with possession of firearms and ammunition by a felon, possession of an unregistered explosive device, manufacturing marijuana, possession of an explosive related to drug trafficking, and possession of a gun in connection with drug trafficking.

If convicted of the first charge, he will be sentenced as an armed career criminal, serve 15 years to life in prison and be fined as much as $250,000. Infante was convicted in Vermont in 1989 of possessing and manufacturing a bomb, and convicted in 1993 of being a felon in possession of a gun.

If convicted of possessing explosives related to drug trafficking, he will face a minimum sentence of 30 years, to be added to the career-criminal sentence, for a total minimum sentence of 45 years.

Infante pleaded not guilty. The assistant federal public defender, J. Hilary Billings, tried to persuade a judge that firefighters shouldn’t have been allowed to search Infante’s home, so any evidence found there should not be allowed at trial.

Infante also argued that investigators had not given him his Miranda warnings, so statements he made to them should not be admissible.

Earlier this year, the judge rejected those arguments. Magistrate Judge John H. Rich III said the firefighters did have “exigent” circumstances to search for the source of the explosion, so their observations — and the search warrant — were legal.

The judge also noted that Infante was not in custody at the hospital, and that Young repeatedly told Infante that he didn’t have to talk to investigators.

Infante waived that right and made voluntary statements, the judge said, among them that he has a fascination with pipe bombs and had made four of them on the morning of the explosion.

The ruling dealt a crippling blow to Infante’s defense. He has agreed to change his plea at a hearing in federal court Thursday. Whether he plans to plead to all of the charges is unclear. A call to his attorney was not returned by press time.

Infante has been held in the Cumberland County Jail pending trial.

Staff Writer David Hench can be contacted at 791-6327 or at: dhench@pressherald.com