Continuity mistake: When Aleksei Sytsevich says his own name and cackles, we see the other marauders jumping on the Oscorp truck. There's a shot from a crossroad with a pedestrian wearing a grey suit that looks at the police car in pursuit, and at the street corner there's a woman by the garbage bin; the camera angle changes and the people at that corner have changed. (00:08:10)
Revealing mistake: In the airplane fight, heavy objects (and people) get sucked out of the door once the cabin is depressurizing, but the cables and the mask tubes on Richard's side stay softly curled and unmoving throughout the scene. (00:06:10)
Other mistake: Richard Parker is running away from Oscorp after triggering an alarm at either 6:30 or 9 PM - the movie is contradictory on which one. He goes home to quickly pack and get his son, and then goes to his brother's place to dump him there. The next scene shows him and his wife discussing the situation, including where to spend the night; they are mid-flight to Wisconsin and it's daylight.
Continuity mistake: When Mary and Richard Parker says goodbye to their son, the scene is similar but also different from the previous movie; she delivers her line with a calmer voice and doesn't stroke his hair in the jittery nervous way of the original. The dad's farewell to Peter is also longer and here they touch hands. (00:02:25)
Continuity mistake: When Peter looks at Gwen's mementos, the photo he had in hand and the USB key both change position between shots. (02:07:50)
Continuity mistake: Peter is absent-mindedly listening to the news while Aunt May is putting away some objects. There's a cut while the speaker says "return of the web-slinger" and May who just had put down some letters is suddenly lifting a book. (02:06:25)
Continuity mistake: The one kid Spidey helped is looking at the window during the news story about Rhino breaking out of prison. He leans forward, but he's in a different position between shots, and his wind turbine is powered up only in the last shot even if it was still two shots before. (02:06:15)
Revealing mistake: As he holds the dead Gwen in his arms, Peter says "Stay with me, stay with me" two times, twice, and then a fifth time "You stay with me." Between the two repetitions, you can see Emma Stone's long eyelashes twitch. (02:02:30)
Continuity mistake: In the final battle, Spidey is going hand-to-hand with Goblin while Gwen is still dangling. At one point he wraps his web around Goblin's neck; the two loops of web change distance depending on the camera angle. (02:00:10)
Continuity mistake: When the sickly kid CEO overpowers the two security guards, he does so with the one on the right that mysteriously in one shot is facing him and in the next he's facing the nearby desk, away from him. (01:33:35)
Audio problem: When Harry listens to the recording of Electro's threats to Dr. Ashley Kafka, the sentence is conveniently edited for brevity, omitting part of the original sentence ("A world without mercy"). (01:15:25 - 01:28:40)
Revealing mistake: Harry Osborn types "Special Projects" (and we see the word taking shape as he types) hitting as the last keys "E", space bar and "G." (01:28:05)
Continuity mistake: When Peter for some reason decides to try to hoodwink the English receptionist pretending to be "John Hopkins", he mentions that he tried to get Gwen to be part of "my team." In that, a guy comes in frame walking from right to left. Several seconds later, same extra, same walk. (01:24:20)
Continuity mistake: During Peter's rant inside the Oxford office, Emma Stone's hair comes and goes from the front of her right shoulder. This happens all the way throughout the scene, even at the pivotal moment at the very end when she asks him which was the "one thing" he mentioned. (01:23:20)
Continuity mistake: Inside Oxford's North American office, Peter starts blathering; he says "Everything's a mess", he says; Emma Stone in the next shot has her hand raised. The mistake happens again at the end of the conversation when Peter goes "I'm sorry to bother you", and her raised hands go down her sides from the wide shot. (01:23:15)
Continuity mistake: When Harry is talking to Spidey that barely camouflages his voice, the hair on his forehead keeps changing position between shots. (01:21:20)
Continuity mistake: Peter inputs in Google "What is Roosevelt?" and gets as output for his search "Franklyn Roosevelt + New York" (01:01:25)
Continuity mistake: Harry wakes up to Spiderman's voice in his living room. He sits and looks at him. Notice the messy hair on his forehead. Changes shot (he is rubbing his nose like Gwen, just not as cute) and his hair is combed over properly. (01:20:50)
Continuity mistake: Peter comes back home and finds his aunt sitting on his bed staring at his serial killer-like collage. The two start talking, and during the conversation May has several locks of hair on or off the cheek as the two angles alternate. (01:16:45)
Continuity mistake: During the kiss in closet scene, Garfield has his hand on Emma Stone's face abruptly at the cut. Seconds later, when they concur that the kiss was "a bit rushed" they smile at each other with a completely different position - as you can see from the light rays on their faces. (01:10:55)
Answer: Peter could have webbed him up and called the police anonymously.
MasterOfAll
Very likely. However, there was a deleted scene in which Peter, out of anger over Gwen's death, almost beats Harry to death.
Yes. We also see Goblin getting knocked out when all hell breaks loose, and the gears all break apart. Chances are, Peter just webbed him up. (Although, as the other response says, he also got beaten up in a deleted scene.)
TedStixon