In a video taken inside a police car, Mulkeen and his partner are singing John Denver's 'Take Me Home, Country Roads' with glee, just minutes before a struggle that led to Mulkeen's death.
"I wish I knew this was the last song we would sing together," Mulkeen's partner Bryan Mayhon wrote in the Facebook video post, "the last time we would be "98" together, the last gun we would grab together."
NYPD leaders said that on Sunday at about 12:30 AM, a group of officers including Mulkeen, 33, were on patrol in the Bronx when they stopped to question two men on 229th Drive North near Edenwald Houses.
One of them, 27-year-old Antonio Lavance Williams, took off running, according to NYPD officials. Mulkeen and another officer caught up with Williams, who police later said was illegally armed with a revolver but did not shoot.
A struggle ensued.
NYPD Commissioner James O'Neill said during a press conference on Monday afternoon that Mulkeen fired his gun five times, and five other officers fired a total of ten rounds.
Two of the rounds hit Mulkeen. Williams was also shot.
They both died at the hospital.
A deputy chief said Williams was holding a revolver which was bought in Richmond, Virginia in 1971 and police are working to find out how it ended up in Williams' possession.
Five out of six officers at the scene of the struggle had body-cameras rolling, O'Neill said, and investigators are currently sorting through the video and other evidence.
"I saw some of the body-worn camera footage, and I got to tell you," Commissioner O'Neill began. "There are 36,000 cops in this police department. Each one of them is incredible human beings, but I'm not sure if everybody would have done that. He displayed incredible, incredible courage."
On Monday, the mayor of Monroe, where Mulkeen grew up, wanted to do something special for the officers who were escorting Mulkeen's body to a local funeral home.
Mayor Neil Dwyer said, as he began arranging 1,500 American flags along the procession route early Monday morning, several passers-by stepped in to help.
"When I put them out, police officers stopped and wanted to help," Mayor Dwyer said, teary-eyed. "The Department of Public Works also came out and put them out. Everybody came out just to help. It's just a testament to people."
Mulkeen had been with the NYPD for seven years and was most recently working in the Bronx Anti-Crime Unit.
He got his start in law enforcement with the Town of Tuxedo Police Department as dispatcher.
While studying at Fordham University, he was a star track and field athlete, winning several honors for the hammer and weight throws. He recently returned to Fordham to serve as a volunteer coach for the track and field team.
Mulkeen's partner, Bryan Mayhon, wrote a few final words on social media accompanying the singing video.
"Watch over us on those country roads," Mayhon wrote. "I know you're home."
According to the Fordham University Sports website, Mulkeen's wake is scheduled for Thursday, from 1:00 p.m. to 4 p.m. and 6:00 p.m. to 9:00 p.m. at Seaman and Quackenbush Funeral Home in Monroe; and the funeral at 11:00 a.m. Friday, at Church of the Sacred Heart, also in Monroe.