LOS ANGELES—FBI agents scrambling for leads after the bombing of a military recruiting station in New York’s Times Square quickly had one in hand—literally.Members of Congress had been receiving letters in recent days that included a photograph of a man standing in Times Square with the words, “We Did It,” printed below the photo. It raised immediate suspicions after the early morning explosion, and the return address on the envelopes was the Hollywood home of lawyer David Karnes.

FBI agents pulled over the Harvard graduate Thursday after he left a workout at a gym, and after questioning him and searching the home investigators concluded he was not involved in the crime. It turned out that “We Did It” referred to the Democratic Party taking control of Congress in 2006.

Neighbors said plainclothes FBI agents sealed off the quiet, hillside neighborhood during the search, flashing badges and urging them to stay indoors.

The episode left Karnes’ shocked, but a day later he was trying to take it in stride, said his mother, Frances Karnes, 82, who lives in Orange County, Calif.

David Karnes did not respond to phone messages Friday, and no one answered the doorbell at his home.

Ironically, he wasn’t aware of the details of the New York bombing.

At first “he was in shock,” his mother said in a telephone interview. “I just spoke to him. He seems quite calm. He realizes it’s going to blow over.”

He’ll be OK. He wasn’t involved,” she said. “My son, he’s a very bright and intelligent man. He would never do anything like that.”

Nonetheless, the episode left the family rattled, since Karnes was as unlikely a bombing suspect as one could imagine.

Karnes, who is single, graduated from Harvard University in 1979. He went on the take a law degree from the University of California, Berkeley, and also earned a doctoral degree there in American history.

The lengthy anti-war letters were sent to as many as 100 members of Congress, officials said. Laura Eimiller, an FBI spokeswoman in Los Angeles, said “there is no evidence linking the letters, which contained no threat, to the bombing.”

Neighbors described Karnes as an outgoing man who liked to talk politics and wasn’t shy about expressing his liberal views. He was so generous, one said, he allowed a neighbor to leave a car in his driveway, no small gift in a city famously short on parking spaces.

Max Roth, a 25-year-old software engineer, used to live two houses away and was visiting the neighborhood Friday. Roth said Karnes was politically active and had tried to enlist him to write letters on political issues.

“He was very politically aware, politically active,” Roth said.

Frances Karnes said the she considered the saga “a big coincidence.”

“It’s just the most amazing thing I’ve ever heard,” she said.