40 years ago today police arrested the Son of Sam, the serial killer who shot six people dead and wounded seven others. NY1 Criminal Justice Reporter Dean Meminger tracked down the NYPD's former top detective, who says like many other New Yorkers, he was fearful, too:.

He was a one-man killing spree who became known as the .44-caliber killer, and then, the Son of Sam.

"People became really afraid — even though it is a big city — that this man could strike anywhere," said John Keenan.

Keenan was the NYPD's chief of detectives at the time. By August of 1977, David Berkowitz, who was Son of Sam, had shot six people dead and wounded seven others.

Although he had a gun and a badge, Keenan felt the same fear as other fathers of the mysterious killer who traveled the city looking for victims, especially young women.

"My daughter Joan was a teenager, and I had two other daughters," Keenan said. "And I was worried about them.

"And I realized most fathers were in the same position: they were worried about their daughters. It became kind of a panic in the city."

The killing spree began in July 1976, when two people in Pelham Bay in the Bronx were shot, one fatally.

Over the following months, Berkowitz would shoot others in similar fashion in that same neighborhood, as well as in Queens and Brooklyn, contributing to a feeling that the city was out of control.

"I don't feel free to go out, to walk the streets, or go out at all," one woman said in 1977.

Berkowitz often targeted young couples sitting in cars late at night. The female would have long, dark hair. Those who fit that profile feared they too could be killed.

"I'm afraid, I'm afraid to go out in the car, I'm afraid to do anything," one woman said at the time. "You never know where he's going to be."

"We used to stay in front of my house and talking and kiss goodnight, but you can't do that anymore," another woman said at the time. "Just go right in."

Berkowitz left a letter that taunted the police, and referred to himself as the Son of Sam. He also sent one to legendary columnist Jimmy Breslin, promising to kill again.

After searching for cars that received parking tickets near the last killing scene in Brooklyn, police tracked down Berkowitz to his home on Pine Street in Yonkers, just north of the Bronx.

Keenan, now 97 years old, vividly remembers Berkowitz immediately confessing to the murders.

"I went up to him, and he said, 'I know you, you're detective — Chief Keenan,' Saw me on television, I think." Keenan recalled. "I said, 'Who are you?' and he said, 'I'm the Son of Sam.'"

"And he went through every one of the crimes, incidents. And he knew, he told us exactly what happened, including information we hadn't released to the press," Keenan said. "So, we knew that it wasn't something he read in the papers. He knew, he was there."

A detective that also worked the case says Berkowitz appeared proud of the murders.

"He was a mental case, and he was very relaxed talking about them," said Bill Clark, a retired NYPD detective. "For all those years, for the time he was doing it, now he could finally tell somebody about it."

Berkowitz pleaded guilty. Now 64 years old, he's serving six consecutive life sentences. He said his neighbor's dog told him to kill.

That neighbor's name was Sam.