If the detective had waited just a few seconds, or missed by a few inches, a man might have died.
It sounds like the start of a mystery novel, but it was reality for an MBTA Transit Police detective Wednesday afternoon.
Sean Conway, the detective, was searching for a suspect in Park Street Station when, he said, he noticed something unusual.
A man was perched on the edge of the Red Line platform, taking sips from a bottle of alcohol and screaming incoherently, he said.
The detective ran from the center platform up the stairs and then down another stairway leading to the southbound Ashmont/Braintree track.
He showed the man his badge and tried to talk to him, he said Thursday.
“I said to him, ‘Step back, you’re going to get hurt,’ ” said Conway, 47. “But from the way he was acting, I knew this wasn’t your average disturbance.”
Once the man, who was in his 40s, spotted Conway, he took another swig from the bottle and attempted to jump down onto the tracks.
Conway grabbed the man’s wrist and swung him to the ground, holding him down. That probably saved the man’s life, police said.
The next train was due in just four minutes. But a more immediate threat came from the third rail and its 600 volts of electricity, directly underneath the platform at that location, police said.
“Without Detective Conway’s work, this man likely would have been electrocuted,” Chief Paul MacMillan said Thursday. “We’re very proud of him.”
Transit police detectives are not trained for such rescues, but Conway rose to the occasion, MacMillan said.
“Our detectives are always observing,” MacMillan said. “They are trained to pay attention. You see that at work here.”
Conway was modest — he said he was not a hero and disliked the attention. But he was happy he was able to intervene.
“Usually, I come after the fact,” Conway said. “I’ll have to do an investigation if someone jumps. But I’m glad this time I could help.”
The man, whose name was not released, was taken to a hospital. Before he left, he thanked Conway.
“I said to him, ‘What did you think you were doing? You could have injured yourself,’ ” Conway said. “And that’s when he said thank you. I was happy about that.”Jacqueline Tempera can be reached at email@example.com. Follow her on twitter @jacktemp.