Just because the government didn't charge someone with murder, doesn't mean they believed he was innocent. It means they didn't have evidence to prove it was murder, or that that person did it.
The standards for evidence that law enforcement must abide by, before they bring murder charges, are very high, quite rightly. They're much more rigorous than the evidence that can be introduced into court by lawyers in a civil action for damages.
Civil lawyers, unlike government prosecutors, can rely on hearsay, innuendo and emotionally-charged re-enactment scenarios, whereas government prosecution against individuals should be based purely on proven facts.
Police and prosecutors have to prove guilt 'beyond a reasonable doubt', whereas in a civil case the jury can decide on a 'balance of probabilities', ie 51% murder vs 49% to suicide.
As well, the government will only bring very strong cases to court, that they really believe they can win. Obviously, it's extremely damaging to someone's life and reputation to be openly accused of murder by the government. Plus, it's considered a waste of taxpayers funds to prosecute someone just because they 'might' be guilty.
Whereas the family who launches a civil action is more obviously just expressing their version and feelings, and agrees to pay the costs themselves if they lose.
The jury in a civil trial is also, IMO, highly influenced to award damages when they are considering whether a rich person should pay money to poorer people who lost a loved one, versus when they are deciding to send someone to jail for the rest of their life.