Legal Question in Criminal Law in California

It is impossible to predict. Every case is different.

Defending someone in a murder case is complicated, and a case can take more than a year to work its way to trial.

I don't know what you mean "by the case is cold, no physical evidence." The District Attorney can take a case to trial on very minimal evidence; whether a jury believes the defendant guilty beyond a reasonable doubt it another matter.

How long? As long as it takes to go through the trial process. In a capital case, possibly several years, then many years of appeals can follow. The average capital case in CA is something like 17 years before appeals are over. He wouldn't be in jail if there was 'no' evidence. The DA wouldn't have filed charges with 'no' evidence; they think they can convict him or they wouldn't have filed. The charges would have been dismissed at Preliminary Hearing is there was 'no' evidence. His attorney's job is to force the DA to prove their case at trial. The jury decides the outcome. Without being sarcastic, most defendants claim to be 'innocent'. Few are. The system is clearly designed to avoid convicting an innocent man.