There is the famous incident known as the Boston massacre which became quite a rallying cry for the revolutionaries. It is believed that 5 people were killed however the details of the incident are portrayed very differently in different contemporary accounts. "A Short Narrative of the Horrid Massacre" was a pro-revolutionary pamphlet which describes the British Soldiers putting down a peaceful protest while the British made "A Fair Account of the Late Unhappy Disturbance in Boston" claims that the soldiers were attacked by violent rioters. The Soldiers were all tried for the incident resulting in two of them being found guilty of man slaughter.

Other than that the waters go a bit more murky, truth is the first casualty of war, it is certainly true that the British and loyalist Americans took supplies from the local population but to be fair to them most armies throughout history have. They did also execute revolutionary soldiers and spies, the captured members of the Crawford expedition for example, but the revolutionaries did that too.

In conclusion I do not have sufficient evidence to say for sure that it did or did not occur but from what I can tell it wasn't a common affair to kill civilians without cause.