How did bagpipe-blowing, at the funeral of a deceased police officer, become a tradition?

Perhaps this may go somewhere towards giving you an answer, although I am in the UK, and here bagpipes would be played if someone came from either Scotland or Ireland.
bagpipes funeral

I believe it actually started with the Fire Departments in cities like NYC. Back in the day, many of the firefighters were Irish and Scots. The connection with police and fire departments (although there is a lot of teasing back and forth) is close (as you, no doubt, have experienced). In my town the bagpipe brigade plays at funerals for both police and firefighters killed in the line of duty. It is a police/fire department group.

In the US, the pipers seem to most often wear the Black Watch tartan probably because it is only loosely associated with a clan and more associated with government forces (going way back in its history).

Here is an interesting article about the role of bagpipes at funerals. It explains that the Irish took the dangerous jobs and when someone died, the Irish funeral traditions were in place and later extended to others who were not Irish. The Scots bagpipes were used because they were louder than the uillean pipes of the Irish.

Question: Why are bagpipes a part of funerals, especially firefighter and police funerals?

Answer: The history of funeral bagpipes is a fairly simple (though very sad) one. In traditional Celtic cultures, including both the Irish and Scottish cultures, bagpipes were an important part of a traditional funeral. After the Great Potato Famine of the mid-1840s, Irish immigrants came to the United States in huge numbers. Due primarily to racism and xenophobia, Irish people were often allowed to apply for only the most dangerous and difficult jobs, including the jobs of firefighter and police officer.

Work-related deaths for firemen and cops were not uncommon, and when one or more of these deaths would occur, the Irish community would hold a traditional Irish funeral, including the mournful bagpipes. Over the years, this tradition spread to firefighters and police officers who were not of Irish descent.

So if it’s an Irish tradition, why are the Scottish bagpipes used?

In short, it’s because the Scottish highland bagpipes are significantly louder than the traditional Irish uillean pipes. Though it’s likely that either or both types of pipes were used at funerals in the 1800s, the Scottish highland pipes are now almost universally used.

Where do they find bagpipers to play at firefighter and police officer’s funerals?

Fire and police departments in most major cities have a special brigade, usually as a division of an Irish fraternal group called The Emerald Society, who learn to play bagpipes and drums for the very purpose of honoring their fallen comrades. In some places, civilians may be members of the pipe and drum band, but generally, the members are active or retired firefighters and police officers. Source

Don’t mess with the Scottish….