Conditions were cramped.
"They slept on the floor on crude little mats. It was so crowded they couldn't even get up and go to the bathroom," McGowan recounted. "I tried to stay out of the way, these people were crammed in there so tight."
"Under her outstanding care, some of those people recovered and got up and walked out," he said.
McGowan said he was "extremely impressed" with her work.
"I think that showed in my writing about her."
His Associated Press account from March 1966 was the first international news story about her.
McGowan said he didn't know if he could even explain what motivated her.
"She always wanted to do the Lord's work, I guess she would say."
"I'm not Catholic, but obviously she is an amazing woman," he continued. "I just have the highest of respect for her, the work that she did, to work there in the slums of Calcutta."
The Indian city was a rough place in the 1960s.
"Calcutta is a place all unto itself," McGowan recollected. "I saw a couple of completely naked women walking the streets, their hair all disheveled. They would see a cigarette butt and they would reach over and pick it up and chew it and eat it. This was the kind of thing you saw in Calcutta in those days. How they are today, I don't know."
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Another time he saw a group of students waiting and waiting for a streetcar, growing increasingly angry at the delay.
"They were so mad, when the street car arrived they set it on fire. That meant fewer streetcars for the next day."
In a world like that, McGowan recalled, Mother Teresa was "very, very calm" and "very unpretentious."
"She was doing all this work, but it was just her life. She wasn't bragging about it."
The people she helped reacted with great appreciation.
"Elsewhere they had not received any aid of any kind," he said. "It was so unusual in an extremely overpopulated place like India for them to get this kind of attention."