You can always walk out of a police interrogation. If you are not allowed to go, you are being interrogated and must read your Miranda rights. You are not free to depart just because you are not under arrest. See, for example, Terry vs. Ohio, where the court said that you cannot be dismissed merely because officers have not yet found enough evidence to charge you with a crime.
However, if you are simply asked to come in and answer some questions, then you are not under arrest and are free to leave at any time.
This does not mean that you can ignore your obligations or avoid giving details about yourself. Any information that you provide may be used as evidence against you in court. But since you are not under arrest, you do not have to stay.
The fact that you have been invited to speak with officers about certain allegations is not an interrogation. It is only when officers start asking questions about other crimes that this becomes an interrogation. For example, if officers ask you about other robberies that have taken place in your neighborhood, this would be an interrogation because it relates to other crimes for which you could be charged. However, if they only want to know about the robbery you reported earlier in the day, this is not an interrogation even if it involves the same officers from earlier. They can only ask you questions about the original crime for which you were arrested/detained.
What to Do If You're Interrogated by the Police
What happens following the interview? You will be allowed to depart after your interview, but only with care. Sometimes the police will be able to tell you what is going to happen right immediately. Typically, the police or the Crown Prosecution Service (CPS) must review the case before deciding how to continue. The interview with a lawyer will usually be conducted by a detective sergeant or less commonly a police constable. The interviewer will probably not be involved in investigating your case so cannot give advice on whether to reply to questions or not. They will simply want to know what you know about the incident.
If you say nothing during this interview, that is all the information the police will have to work with. They may still decide to charge you, but that would be at their own discretion. If they do choose to proceed with charges, you would then receive legal counsel from the National Crime Agency (NCA), who would also ask you some more questions. Once the NCA has completed its investigation, then it would make a recommendation to the CPS as to whether there are grounds to prosecute or not. If there are grounds to prosecute, then the CPS would issue an indictment which would lead to court proceedings.
In conclusion, after being interviewed by the police under caution, you should be free to go about your business while they investigate the case further. Do not talk to anyone else besides your lawyer and any police officers that are involved in the investigation.
You cannot be arrested if there is no proof. A police officer must have probable cause to arrest someone for a criminal conduct. It occurs when a police officer has built a case to the point that a reasonable, cautious officer would conclude the accused is guilty. Officers need not always find evidence that would hold up in court to make an arrest. For example, an officer may believe based on eyewitness accounts from multiple people that a crime has been committed and therefore have reason to arrest the suspect.
There are times when officers have reason to believe that a person has committed a crime but lack the evidence to support an arrest. For example, an officer may have seen a car drive through a red light but cannot prove who was driving because the driver left before police arrived. In this case, the officer can still take action against the driver by citing him or her for traffic violation. If the driver does not contest the citation in court, he or she will be given a fine as punishment for the offense.
Detention rather than arrest is used when it is not feasible or appropriate to bring a suspect into a police station. For example, if an offender is wanted for murder and is found hiding under a bed, it would be inappropriate to stop him or her from continuing to flee the scene. Instead, authorities could place the suspect under arrest for obstruction of justice or some similar crime.
It makes little difference whether an interrogation takes place in a jail, at the site of a crime, on a busy downtown street, or in the middle of a field: If a person is detained (deprived of considerable freedom of action), the police must read the Miranda rights if they wish to ask inquiries and utilize the Miranda warning. Asking questions without reading the rights is considered coercive and violates the spirit of the rule.
The police are not required to read the rights before each question as long as the reading and questioning occur within a reasonable time period. For example, if a suspect asks when he will be able to leave and the police say he cannot be released until his identity is cleared up, it would be permissible for the police to continue their inquiry after reading the rights.
However, if the police were to question the suspect again two hours later without first reading him his rights, that second interview would be deemed illegal under Miranda.
In addition, if the police fail to read the rights within a reasonable time period or refuse to repeat them before each question, the entire interview becomes invalid and any statement made by the suspect during this period cannot be used as evidence against him.
Finally, even if the Miranda warnings are given and understood, the suspect still has the right to refrain from answering questions. The police cannot force him to speak unless they have probable cause to believe he committed a crime, including murder.