(CNN) - Another New York Police Department officer has died by suicide -- becoming the ninth to do so this year -- a law enforcement official told CNN on Wednesday.
The 56-year-old officer was off duty and at home, according to two law enforcement sources. He was a 25-year veteran of the NYPD who worked in Queens, the official said.
On Tuesday, another law enforcement official told CNN that an eighth officer had died by suicide -- a 35-year-old temporarily assigned to a detail surrounding Yankee Stadium.
That officer, a seven-year veteran, left a note behind, the official said. He was off-duty at the time, two law enforcement sources told CNN.
Of the nine NYPD officer suicides in 2019, seven have happened since June. The recent cluster has rattled the department, with leaders trying to come up with a way to tell the rank and file that it's OK to ask for help.
Over the past five years, the NYPD has averaged between four and five suicides a year, Police Commissioner James O'Neill said in June at a news conference called after the department surpassed its average.
"Tonight our city mourns a tragedy. We won't let anyone struggle alone," New York City Mayor Bill de Blasio tweeted Wednesday night. "I want every one of New York's Finest to know we are here for you. We value you. Help is available. Please reach out."
NYPD has been working on a suicide prevention plan
Since the suicides this summer, the NYPD has been developing a plan to help troubled officers.
Some 800 members of executive New York Police Department staff will begin retraining this month with experts on mental health, stress and suicide, with the goal of eventually training the entire department, O'Neill told CNN during a recent interview at his office in Manhattan.
NYPD staffers also went to Los Angeles and observed its police department peer support system, which includes clinicians who spend time with officers and psychologists who make rounds, visiting every command.
The goal is to have a peer representative in every precinct and every command who's specifically trained to help an officer step back from the brink and find a trained professional to help.
This summer's string of suicides began in June, when a respected deputy chief and an experienced detective died within 24 hours of each other. Days later, a 29-year-old police officer with six years on the job killed himself behind the NYPD precinct in Staten Island where he worked. On June 26, a 53-year-old officer died of a self-inflicted gunshot wound during a family gathering at his home in Hicksville, New York.
On July 27, a 30-year-old NYPD sergeant was found dead in his home from a self-inflicted gunshot wound.
Study: Police more likely to die by suicide than on duty
Police officers and firefighters are more likely to die by suicide than in the line of duty, according to a 2018 study by the Ruderman Family Foundation, a Boston-based nonprofit that advocates for social justice.
In 2017, there were at least 140 police officer suicides and 103 firefighter suicides, compared with 129 police officers and 93 firefighters who died in the line of duty, the study found.
The study found that first responders failed to seek help because of the stigma of seeking mental health treatment in a profession that prioritizes bravery and toughness. It also found of the 18,000 law enforcement agencies across the country, "approximately 3-5% have suicide prevention training programs."
CNN's Mark Morales, Chelsea J. Carter and Jason Hanna contributed to this report.
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