Son murdered outside nightclub parking lot

From the criminal side - there is no statute of limitations in any state for murder; from the civil side - there is a 2 year statute of limitations for wrongful death.

There are two different types of lawsuits that are possible here, a criminal prosecution to send the murderer to prison or death row, and a civil suit for money damages for wrongful death.

I'm not a Texas lawyer, but my research suggests that, like most states, Texas has no statute of limitations on a murder prosecution.  Whoever is guilty of murdering your son can be prosecuted literally as long as he's still alive.  Unfortunately, it also looks like the limitation on filing a wrongful death lawsuit is two years, which has now run out.