In responding to a serious crime in progress such as this, officers are strongly encouraged to coordinate their approach so that at least two officers arrive on scene within seconds of each other.
However, it does occasionally occur that a solo officer comes upon a crime in progress. He doesn't have the luxury of retreating or laying back until backup arrives. He has to act. There's risk associated with this job; that's a given that we all accept.
Radioing out and requesting backup is primary, but what happens after that will depend on the individual situation, surroundings, and a host of other things that the officer will have to assess in seconds, and act accordingly. This is where training comes in.
Usually, when a cop shows up in a marked unit, someone yells "five oh!" and everyone splits
. If that doesn't happen, you know automatically you're going to have a fight on your hands, weapons or not. At this point, in something as serious as a carjacking, the officer should escalate immediately to a point/aim with his weapon and issue verbal orders.
If the suspect doesn't comply and flees, Tennessee vs. Garner would apply and deadly force would be justified (although in most cases, a foot pursuit would ensue to attempt an apprehension.) If the suspect physically confronts the officer, he (officer) is going to have to make a split second judgment of whether or not he has a reasonable and justified fear for his life. If he does, deadly force is justified. This would be especially true if the BG's friends decide to get in the act. Then you try to delay and detain until backup arrives, and most importantly, watch your six. You don't want to get surrounded.
In this case, after the arrest was made would be one of the toughest times for any officer. Believe it or not, cops are human too
, and the desire to beat the crap out of that slime-bag would be overwhelming. Most though, would remember that they're professionals, curb their emotions, and do their jobs honorably, and for that alone, they should get a medal.