Suddenly
No Punting
The reason lawyers generally advise their clients not to testify in criminal trials is not because they 'know' or 'think' they're guilty, but because they know that a good prosecutor can confuse a defendant making them contradict themselves or appear like they're lying.
That and it can be used to narrow down facts leading to a false conviction.
Say the cops need to prove two acts to establish guilt. They have some questionable evidence of one act that points towards a person who did not in fact perform that act.
However, that person did perform the second act. The cops have no evidence whatsoever of this.
If our person confesses to that second act it would "tend" to incriminate them in that it would create the illusion that it was more likely they were also the person who performed the first act.
Which is why it is a very bad idea (at least in the US) to talk to police without a lawyer who understands this larger picture.