Ex-Oakland Raider -- Gets Life In Prison ... For Killing 3 Men

Former Oakland Raiders defensive end Anthony Smith was just sentenced to 3 consecutive life sentences for killing 3 men between 1999 and 2001 ... TMZ Sports has learned.

We previously reported ... Smith -- who played for the Raiders from '91 to '97 -- was found guilty of kidnapping two brothers -- Kevin and Ricky Nettles -- from a car wash in 1999 and then shooting them to death. Their bodies were dumped roughly 8 miles apart.

In 2001, cops say Smith was part of a group that kidnapped Dennis Henderson and then stabbed him to death.

Smith appeared in an L.A. County Superior courtroom Friday -- where the judge threw the book at him, sentencing him to life in prison for each of the 3 murders without the possibility of parole.