Left, Associated Press; Right, James Barron/The New York TimesThe rubble at 18 West 11th Street after the blast in 1970, and the address today. The town house was a bomb-making site for the Weathermen, a radical group also known as Weatherman and as Weather Underground.

Charles LockwoodWest 11th Street moments after an explosion in a town house that had been used by the Weathermen.

A City Room post recently about a town house on the Upper East Side that blew up in 2006 brought to mind another town house, another era and another explosion — the town house in Greenwich Village that became a bomb factory for the radical group the Weathermen.

Unlike with the physician on the Upper East Side who apparently intended to destroy his town house, the explosion on West 11th Street in Greenwich Village, in 1970, was an accident.

Charles Lockwood remembers how loud it was. He was down the street, taking pictures.

He was a senior at Princeton. He and a classmate with a new camera had driven to Manhattan to take photographs for Mr. Lockwood’s senior thesis. It served as the basis for his book “Bricks and Brownstone: The New York Row House,” published in 1972 and reissued by Rizzoli in 2003.

They had set up their tripod by the parked cars down the block and were focusing on a Greek Revival doorway when the blast went off. Mr. Lockwood said they were thrown by the force of the explosion but were not knocked down. As smoke streamed from the town house, they ran up the street and snapped about a dozen photos, unaware that three people lay dead inside or that two women had fled.

Neither of the women had much on in the way of clothes as they ran out. One had apparently been taking a shower, and the other had been ironing. As the fire trucks pulled up, a neighbor let them in to clean up and gave them clothes. Then they left, coolly heading to the subway.

Before long, the details of the bomb-making emerged. “Shortly after that,” Mr. Lockwood recalled recently, “I started getting visits — one from the New York Fire Department and two from the F.B.I.” His friends at Princeton were nonchalant. The Federal Bureau of Investigation agents found him at his eating club. The second time they showed up, someone yelled, “Charlie, the F.B.I.’s here again.”

“The F.B.I. was particularly curious if I had seen two naked women running from the house,” Mr. Lockwood said. “They kept asking, ‘Did you see the naked girls?’ I told them no, I hadn’t. What I was really worried about was the rest of the block would blow up while we were standing there. I didn’t see Dustin Hoffman, either.”

Mr. Hoffman had lived next door. The living room wall of his apartment had been blown open. His desk had tumbled into the wreckage.

The two women, Cathlyn Platt Wilkerson and Kathy Boudin, remained at large for the rest of the 1970s. Ms. Wilkerson turned herself in in 1980 and wassentenced to three years in prison. Ms. Boudin was arrested in 1981 after an armored-car holdup in Rockland County that left three dead: two police officers and a Brink’s guard. She pleaded guilty in 1984 and was released in 2003.

As for the town house that was destroyed, it dated to the 1840s. It had once been owned by Charles Merrill, a founder of Merrill Lynch. He called it “the little house on heaven street,” which sounded like a line that could have come from the man he sold it to, Howard Dietz, a Broadway lyricist and movie publicist. Ms. Wilkerson’s father, James, had bought it in 1963.

After the rubble was cleared, the vacant lot was sold for $75,000 to the architect Hugh Hardy and Francis Mason, a dance devotee and critic who was working as an assistant to Arthur A. Houghton Jr., the president of Steuben Glass and chairman of the Metropolitan Museum of Art.

Mr. Hardy said the idea originated with his wife, Tiziana. “Tiziana said, ‘Why don’t we buy the land, and you can design the house?’” he recalled last week.

He said he remembered thinking, “Oh, no.”

He designed a two-family structure that was “much less confining than a conventional brownstone.” The idea was for the Masons and their children to take the bottom two floors and the garden and for the Hardys and their children to have the top two floors and a terrace.

His design matched the height and scale of the houses on either side, but had a angular facade that jutted out toward West 11th Street. “It was this whole idea that a new building should express something new,” he said, adding, “We were deeper into diagonals at that point.”

He went before the Landmarks Preservation Commission to convince it that his design was “appropriate” for the site and won approval after agreeing to some changes.

“We couldn’t build it,” Mr. Hardy said. “We went to the bank to try to get a mortgage. This guy says: ‘I can see you’re a nice young man. I could give you a mortgage. There are wonderful houses in’ — he named some part of the East Village — ‘but I am not going to give you a mortgage on any of those places.’”

The man mentioned Westchester County, Mr. Hardy said, adding: “He had redlined all of Manhattan. I got so angry I almost hit him.”

They sold the lot, and the new owners built the house.

Mr. Lockwood went back to Princeton and finished his thesis. He said it contained not a word about the bombing.

“No,” he said. “I remember my faculty adviser getting a kick out of it, but that was about it except for ‘Hey, Charlie, the F.B.I.’s here.’ I turned in my thesis. I won a prize for the thesis. That led to getting a grant, 16 to 18 months of money so I could turn the thesis into a real book.”