The 53-year-old unnamed off-duty officer was found dead at his home in Hicksville. He was assigned to the 50th Precinct in the Bronx.
Monahan said the death was the fourth this month, and the sixth this year. He also said the officer's death marked the 101st in the country this year.
"We have to figure out a way how we can save our own lives," he said.
He also said officers needed to be treated better when they do come forward.
"Once they are well they will be back on the street," he said.
Police Commissioner James O'Neill has declared a mental health crisis in the department after the three previous suicides in June and has sent messages reminding officers to seek help and to utilize the services available to them.
In a statement on June 14, O'Neill said: "There is no shame in seeking assistance from the many resources available, both inside and outside the department. Accepting help is never a sign of weakness — in fact, it's a sign of great strength."
The other deaths included Deputy Chief Steven Silks, found dead in a police vehicle on June 5, the next day, Detective Joseph Calabrese, found at a Brooklyn beach and, Michael Caddy, 29, was found on Staten Island, on June 14.
For help, officers are encouraged to contact the Employee Assistance Unit at 646-610-6730, the Chaplains Unit at 212-473-2363, and the Police Organization Providing Peer Assistance at 888-267-7267.
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