At 3:50 p.m. Friday afternoon, a 29-year-old New York City police officer shot and killed himself outside the Staten Island Police precinct where he worked.

It marked the latest in a troubling trend: three suicides of New York Police Department officers in 10 days – and the fourth this year.

The deaths in New York are part of a national problem. Last year, for the third straight year, cops who died by suicide outnumbered line-of-duty deaths.

New York's string of tragedies prompted NYPD Commissioner James O'Neill to deliver a call for action and to encourage fellow cops to not be afraid to seek help if they need it.

"This is a mental-health crisis," O'Neill tweeted Friday night. "And we – the NYPD and the law enforcement profession as a whole – absolutely must take action. This cannot be allowed to continue. Cops spend so much of their days assisting others. 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," he added. "In fact, it's a sign of great strength."

The NYPD has not released the name of the latest police officer who died from suicide.

A funeral was held Monday for Steven Silks, a 62-year-old deputy police chief who shot and killed himself in a car on June 5. The New York Times reported that Silks, a 38-year veteran of the department, parked his car on a quiet street just hours after his mandatory retirement was announced. He shot himself near where his retirement ceremony would have taken place.

His death rattled many in the department.

"Steve truly was one of the most capable and most dependable cops this job has ever seen," O'Neill said. "His entire career, much of his adult life in fact, was devoted to New York City, to its police officers and to fighting crime and to protect all the people that we serve."

The day after Silks's death, June 6, Detective Joseph Calabrese, 58, a member of the force for 37 years, went missing. His car was found off Belt Parkway in Brooklyn, The New York Times reported. After a widespread search, he was found dead in nearby bushes at Plumb Beach with a self-inflicted gunshot wound to the head.

"Det. Joseph Calabrese kept New Yorkers safe for nearly four decades," Police Chief Terance Monahan tweeted after his burial Wednesday. "Loved by his fellow cops, the loss of Joe is difficult for every member of the NYPD. As he’s laid to rest, our prayers are with his family. Joe’s death has ignited a conversation we must all continue. #StopSuicide"

In 2018, 159 police officers in the USA died from suicide, according to the Massachusetts-based nonprofit BlueH.E.L.P., which tracks officer suicides while also seeking to prevent such tragedies from occurring.

That's 9% more than the 144 line-of-duty deaths in 2018. The latter includes include causes such as felonious assaults, patrol vehicle accidents, heart attacks and duty-related illness.

“As tragic as these duty deaths are, the single greatest cause of death for law enforcement officers each year is suicide,” Jeff McGill, co-founder of Blue H.E.L.P, said when the group released the 2018 figures.

The number of suicides last year matched the 159 who took their lives in 2017. In 2016, 140 police officers in the U.S. died by suicide.

Blue H.E.L.P. works to expand police officers’ access to mental health services.

Its organizers say that 151 of the suicides last year were male and eight were female. The average age was 41 years old, and the average length of service in the police force was 15 years.

But according to Steven Hough, co-founder of Blue H.E.L.P., the number of police suicides is likely greater.

“The problem is we know there are other tragic deaths by suicide that we don’t know about,” Hough was quoted saying this year. “So as bad a number as we have this year, we’re saddened by the fact that we know in reality the number is higher.”

Reach Joey Garrison at jgarrison@usatoday.com and on Twitter @joeygarrison.