Once you get the time card from the security guard (he's at the Clown Store) you can check the surveillance video for the likely time, and get a photo of the thief.
Night
night right after you get caught the thief is the investigator
hang from the light above it
After you get out of jail, get the time card from the Clown Store and go to the Security Room in the Museum. You can get a photo of the thief from the surveillance videos. Show it Downtown.
You examine the surveillance video at the Security Room in the museum. But you need an idea of the time of the theft. Go to the clown store and get the time card from the guard.
The scooter is just a part of the chase of the shady guy (thief) through the streets of Counterfeit Island. You go from the Jazz cafe downtown to the docks. There is no way to catch him, but you must avoid the open sewer manholes in the road. There is no way to get the scooter at any other time.
There is no key to find. You will get it when the time comes. After you chase the thief, you will be going to the Art Museum on Early Poptropica. You will talk to the curator and she will give you the key.
After the painting is stolen, you will find the security guard at the Clown Store. He has his time card that shows when he left the gallery. Get it and you can find a photo of the thief on the museum's Security Room videos.
Walk over and talk to him. He doesn't have much to say. The only time he is helpful at all is if you ask him where to look for the thief, and he suggests asking the mimes Downtown.
He was caught by the museum security cameras. Get the guard's time card (he's at the Clown Store) and you can print a photo in the museum Security Room. Show it to the mimes at Downtown.
He's in the clown store, trying to cheer himself up. If you talk to him, he will give you his time card. You can use it to find the thief on the video at the museum's Security Room.
The timecard from the missing security guard (at the Clown Store) tells you what time he left the gallery. In the museum Security Room, go over the video to get a photo of the thief stealing the painting.