In the last week alone there have been three high-profile encounters between police officers and knife-wielding suspects. Two of these incidents took place in the US, and both of those ended in the death of the suspects at the hands of officers. The third incident, in the UK, ended with an arrest. Each incident has a corresponding video that gives more details about each situation.

While none of these events are black and white since suspects all had weapons, they do raise questions about when fatal force should be used by police.

The first incident took place on December 2nd. Mario Woods, who was suspected of an assault earlier in the day, was shot dead by several San Francisco police officers. Police said that they had asked him to drop the knife he was holding, and initially used bean bag guns, but to no avail. When Woods began walking away from officers, a flurry of gunshots can be heard.

At a press conference Police Chief Greg Suhr said that his officers could not allow the suspect to leave because he had already proven that he "was a danger to others." However, many believe the video demonstrates that the officers were not in any imminent danger.

The second incident took place in Miami over the weekend. A shirtless suspect believed to have tried to rob a bank was gunned down by officers. After fleeing into a barbershop he walked outside, where he was met by a group of police officers who spoke to him for more than a minute. The suspect, who was holding a straight razor, then put his hand on a police cruiser and pointed the razor in the direction of an officer. In the video it appears that one officer shot a long-range Taser at the man, which was immediately followed by two shots from another officer. The man died at the scene.

The third incident also occurred over the weekend, in London. Another man who allegedly had a knife was in a subway station, where he had injured two people and was continuing to threaten others. According to witness reports the man shouted, "This is for Syria," which has led officials to call this a terrorist incident. London officers however, unlike those in the US, Tased the man and arrested him.

While the situations are similar, it must be noted that circumstances do vary. Officers and police consultants told INSIDER that it is hard to compare situations, because each place has a different protocol.

Still, these incidents raise questions about when force should be used by officers, and whether officers in the UK have different procedures in place that could make a life and death difference. Perhaps US cops could learn a thing or two from them.

Story and editing by Andrew Fowler