NYPD officer Gregory Santora may have saved a fellow officer’s life—and he didn't even have to leave his home to do it.

Santora was off duty the morning of Aug. 6 but on a very special assignment: His 5-year-old daughter, Addison, wanted him to look on his phone for livestream videos from Disney World, where the family is planning to visit.

As he searched his phone using the Periscope app he stumbled upon a disturbing clip of a distraught man who was drinking alcohol and vowing to kill a cop in Madison, Wis., to avenge the fatal police shooting there of Tony Robinson, an unarmed black man he called his “brother.”

Santora immediately thought back to the 2014 executions of Brooklyn Officers Wenjian Liu and Rafael Ramos, ambushed in their patrol car by a gunman who boasted on Instagram that he was going to put “wings on pigs.”

He Googled the phone number for the Madison Police Department, got a dispatcher on the phone, identified himself, then methodically described what he was seeing on the livestream.

He sent Madison authorities links to the Periscope videos posted by a suspect, identified as Raynarldo Glenn, 27, and filled them in as Glenn got even more emotional — crying, vowing vengeance and eventually leaving his house. Glenn got in his car.

“He was actually strapping the guns on,” Santora said, his voice trembling as he recounted what he saw on the video. “And he said, ‘I’m gonna commit suicide by cop.’

In Madison — more than 900 miles from New York — officers were getting updated in real time on their radios.

One officer, Gregory Rossetti, recognized Glenn from the description provided by Santora — black baseball cap, red bandana — and was able to coax him into a peaceful surrender in a hospital parking lot. Two BB guns and a knife were found in Glenn’s car, the New York Daily News reports.