Plainclothes and off-duty police officers have been killed by other officers. It is always a tricky situation when the on-duty crew shows up. You’d have to go into the details of each incident but it’s best to holster the weapon and show your hands.
That being said, it sure looks like there’s an increasing tendency to shoot first and ask questions later. Maintaining cover and taking a couple of seconds to assess the situation would help.
Then there are incidents like this: