NEW YORK -- All it took was some basic piping know-how.

---

Images: Building Reduced To Rubble

More: E-Mail: 'I Will Leave The House Only If I Am Dead'

---

Plastic tubing, connected to a basement main line, allowed gas to flow freely into an Upper East Side landmark for hours, until it set off a violent explosion that cast fireballs into the sky and leveled the town house, a building that had become the focus of a bitter divorce dispute, authorities said Tuesday.

"We're saying this is intentional," Louis Garcia, the city's chief fire marshal, said at a briefing near the scene of the explosion. "Anybody who is handy could do this," he added later.

Garcia detailed how someone had attached the flexible tubing to the main gas line with the help of a brass radiator valve before the Monday morning explosion.

Authorities have been investigating whether Dr. Nicholas Bartha, the lone occupant during the blast, might have caused the explosion rather than sell the town house as part of a divorce judgment favoring his ex-wife. Bartha, a physician who lived and worked in the four-story building, remained in critical condition after being rescued from the rubble.

Detectives "want to talk to him, but haven't been able to because the extent of his injuries," said NYPD spokesman Paul Browne.

Bartha, 66, became a possible suspect after police got a 911 call from his ex-wife, Cordula Bartha. She told them that shortly before the explosion he had sent her a rambling e-mail saying she would soon would be "transformed from gold digger to ash and rubbish digger."

The husband went on by warning her, "You always wanted me to sell the house. I always told you I will leave the house only if I am dead."

The ex-wife's lawyer, Polly Passonneau, said in an e-mail Tuesday that her client was not a "gold digger." Passonneau said the doctor was the one who appealed a lower court ruling that stated the house was not marital property and belonged to him. But he lost the house when a higher court ruled it was marital property.

"He unfortunately did not want to give her one penny, so he kept fighting," Passonneau wrote. "He is living with the consequences of his own behavior."

The explosion left the upscale block covered in bricks, broken glass and splintered wood. Authorities said at least 15 people were injured, including five civilians and 10 firefighters.

The 19th-century town house on 62nd Street between Park and Madison avenues -- just a few blocks from Central Park -- once served as a secret meeting place for a group of prominent New Yorkers who informally gathered intelligence for President Franklin D. Roosevelt before and during World War II.

The building and land were worth nearly $6.4 million, according to the city's finance department. It was to be sold at auction in October to pay a $4 million judgment against Bartha, though his ex-wife had predicted he wouldn't leave without a fight.

"He has said many times that he intends to 'die in my house,"' Cordula Bartha said in a petition filed last year.

The court records paint a picture of a bitter dispute that dragged on for five years.

According to a 2005 appellate court opinion, the doctor had "intentionally traumatized" his Jewish wife, who was born in Nazi-occupied Holland, by posting "swastika-adorned articles and notes" around their home. The opinion also said Bartha had "ignored her need for support and assistance while she was undergoing surgery and treatment for breast cancer."

Power company Consolidated Edison had been at the building on June 8 after a routine check found a gas leak in the pipe.

The gas was shut off, and Nicholas Bartha was asked to get the pipe fixed, a spokesman said. The gas was turned back on after the utility ensured the leak was fixed.