In order to make a valid arrest, the police need probable cause, which is sufficient evidence to give a reasonable person enough proof that, more likely than not, the accused committed the crime. The standard for proving a person guilty is much higher than that. In order to prove a person guilty of a crime, the government must prove guilt beyond a reasonable doubt. This explains why a person can be validly arrested, yet not be proven guilty in court.
In order to arrest you, the police need probable cause that you committed the theft. That can be based on allegations, circumstantial evidence, eyewitnesses, video, or just about anything relevant. In order to convict you, they need proof beyond a reasonable doubt. That is why it is important to get yourself an attorney right away so that he can hold the prosecutor to that high burden of proof and you don't get railroaded. Feel free to contact me at my website below if you have any questions.
They only need probable cause to arrest you, the guy's word may be enough. However, they will need much more than his word to convict you.
THESE COMMENTS ARE NOT LEGAL ADVICE. They are provided for informational purposes only. Actual legal advice can only be provided after consultation by an attorney licensed in your jurisdiction. Answering this question does not create an attorney-client relationship or otherwise require further consultation.